1598349360
During the development and testing of Datona Labs’ Solidity smart data access contract (S-DAC) templates, we often need to handle data with a small but unknown number of items, such as user IDs. Ideally, these are stored in small dynamic arrays of small values.
In the examples for this article, we investigate whether using dynamic value arrays helps us to do that more efficiently than using reference arrays or similar solutions in Solidity.
Where we have data comprising a known small number of small numbers, we can employ a value array in Solidity, as per the article “Value Arrays in Solidity” by the author, in which we provide and measure Solidity value arrays. We concluded, amongst other things, that we can reduce my storage space and gas consumption using value arrays in many circumstances.
This conclusion was reached because Solidity runs on the Ethereum Virtual Machine (EVM) which has a very large machine word of 256bits (32bytes). This feature, combined with high gas consumption for reference array handling, encourages us to consider using value arrays.
However, if we are providing our own libraries for fixed value array manipulation, let us determine whether it is feasible to provide dynamic value arrays as well.
Let us compare dynamic value arrays with fixed value arrays and Solidity’s own fixed and dynamic arrays.
We shall also compare a struct containing a length and a fixed array, as well as a struct containing a value array.
In Solidity, it is only possible to have dynamic storage arrays. Memory arrays have a fixed size and are not permitted to use push()
in order to append additional elements.
Since we are providing our own code for dynamic value arrays in Solidity libraries, we can also provide push()
(and pop()
) to be used on both storage and memory arrays.
Dynamic value arrays will need to record and manipulate the current length of the array. In the following code, we have chosen to store the length in the top bits of the 256bit-, 32byte-machine word value.
These are dynamic value arrays that match some of the Solidity available types:
Dynamic Value Arrays
Type Type Name Description
uint128[](1) uint128d1 one 128bit element value
uint64[](3) uint64d3 three 64bit element values
uint32[](7) uint32d7 seven 32bit element values
uint16[](15) uint16d15 fifteen 16bit element values
uint8[](31) uint8d31 thirty-one 8bit element values
We propose the Type Name as shown above, which is used throughout this article, but you may find a preferable naming convention.
We will be looking at uint8d31 in more detail, below.
Obviously, there more possible value arrays. Assuming that we are reserving the top bits of the 256bit value to hold the maximum dynamic array length, the number of bits in the X value multiplied by the number of Y elements must be less than or equal to 256 minus enough bits to hold the array length, L:
More Dynamic Value Arrays
Type Type Name Len Description
uintX[](Y) uintXdY L X * Y <= 256 - L
uint255[](1) uint255d1 1 one 248bit element value
uint126[](2) uint126a2 2 two 124bit element values
uint84[](3) uint84d3 2 three 82bit element values
uint63[](4) uint63d4 3 four 62bit element values
uint50[](5) uint50d5 3 five 51bit element values
uint42[](6) uint42d6 3 six 42bit element values
uint36[](7) uint36d7 3 seven 36bit element values
uint31[](8) uint31d8 4 eight 31bit element values
uint28[](9) uint28d9 4 nine 28bit element values
uint25[](10) uint25d10 4 ten 25bit element values
uint22[](11) uint22d11 4 eleven 22bit element values
uint21[](12) uint21d12 4 twelve 21bit element values
uint19[](13) uint19d13 4 thirteen 19bit element values
uint18[](14) uint18d14 4 fourteen 18bit element values
uint16[](15) uint16d15 4 as above
uint15[](16) uint15d16 5 sixteen 15bit element values
uint14[](17) uint14d17 5 seventeen 14bit element values
uint13[](19) uint13d19 5 nineteen 13bit element values
uint12[](20) uint12d20 5 twenty 12bit element values
uint11[](22) uint11d22 5 twenty-two 11bit element values
uint10[](25) uint10d25 5 twenty-five 10bit element values
uint9[](27) uint9d27 5 twenty-seven 9bit element values
uint8[](31) uint8d31 5 as above
uint7[](35) uint7d35 6 thirty-five 7bit element values
uint6[](41) uint6d41 6 forty-one 6bit element values
uint5[](50) uint5d50 6 fifty 5bit element values
uint4[](62) uint4d62 6 sixty-two 4bit element values
uint3[](83) uint3d83 7 eighty-three 3bit element values
uint2[](124) uint2d124 7 one-hundred & twenty-four 2bit EVs
uint1[](248) uint1d248 8 two-hundred & forty-eight 1bit EVs
The array type needed is project-specific. Additionally, multiple array types may be needed, for instance, uint8d31 for user IDs and uint5d50 for roles.
Note the uint1d248 value array. That allows us to efficiently encode up to 248 one-bit element values, which represent booleans, into one EVM word. Compare that with Solidity’s bool[248] which consumes 248 times as much space in memory and even eight times as much space in storage.
#ethereum #blockchain #solidity #smart-contracts #programming
1670560264
Learn how to use Python arrays. Create arrays in Python using the array module. You'll see how to define them and the different methods commonly used for performing operations on them.
The artcile covers arrays that you create by importing the array module
. We won't cover NumPy arrays here.
Let's get started!
Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.
Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.
Lists are one of the most common data structures in Python, and a core part of the language.
Lists and arrays behave similarly.
Just like arrays, lists are an ordered sequence of elements.
They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.
However, lists and arrays are not the same thing.
Lists store items that are of various data types. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.
As mentioned in the section above, arrays store only items that are of the same single data type. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.
Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the array module
in order to be used.
Arrays of the array module
are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.
They are also more compact and take up less memory and space which makes them more size efficient compared to lists.
If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.
In order to create Python arrays, you'll first have to import the array module
which contains all the necassary functions.
There are three ways you can import the array module
:
import array
at the top of the file. This includes the module array
. You would then go on to create an array using array.array()
.import array
#how you would create an array
array.array()
array.array()
all the time, you could use import array as arr
at the top of the file, instead of import array
alone. You would then create an array by typing arr.array()
. The arr
acts as an alias name, with the array constructor then immediately following it.import array as arr
#how you would create an array
arr.array()
from array import *
, with *
importing all the functionalities available. You would then create an array by writing the array()
constructor alone.from array import *
#how you would create an array
array()
Once you've imported the array module
, you can then go on to define a Python array.
The general syntax for creating an array looks like this:
variable_name = array(typecode,[elements])
Let's break it down:
variable_name
would be the name of the array.typecode
specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type.elements
that would be stored in the array, with each element being separated by a comma. You can also create an empty array by just writing variable_name = array(typecode)
alone, without any elements.Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:
TYPECODE | C TYPE | PYTHON TYPE | SIZE |
---|---|---|---|
'b' | signed char | int | 1 |
'B' | unsigned char | int | 1 |
'u' | wchar_t | Unicode character | 2 |
'h' | signed short | int | 2 |
'H' | unsigned short | int | 2 |
'i' | signed int | int | 2 |
'I' | unsigned int | int | 2 |
'l' | signed long | int | 4 |
'L' | unsigned long | int | 4 |
'q' | signed long long | int | 8 |
'Q' | unsigned long long | int | 8 |
'f' | float | float | 4 |
'd' | double | float | 8 |
Tying everything together, here is an example of how you would define an array in Python:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
Let's break it down:
import array as arr
.numbers
array.arr.array()
because of import array as arr
.array()
constructor, we first included i
, for signed integer. Signed integer means that the array can include positive and negative values. Unsigned integer, with H
for example, would mean that no negative values are allowed.Keep in mind that if you tried to include values that were not of i
typecode, meaning they were not integer values, you would get an error:
import array as arr
numbers = arr.array('i',[10.0,20,30])
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
# numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer
In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.
Another way to create an array is the following:
from array import *
#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])
print(numbers)
#output
#array('d', [10.0, 20.0, 30.0])
The example above imported the array module
via from array import *
and created an array numbers
of float data type. This means that it holds only floating point numbers, which is specified with the 'd'
typecode.
To find out the exact number of elements contained in an array, use the built-in len()
method.
It will return the integer number that is equal to the total number of elements in the array you specify.
import array as arr
numbers = arr.array('i',[10,20,30])
print(len(numbers))
#output
# 3
In the example above, the array contained three elements – 10, 20, 30
– so the length of numbers
is 3
.
Each item in an array has a specific address. Individual items are accessed by referencing their index number.
Indexing in Python, and in all programming languages and computing in general, starts at 0
. It is important to remember that counting starts at 0
and not at 1
.
To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.
The general syntax would look something like this:
array_name[index_value_of_item]
Here is how you would access each individual element in an array:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element
#output
#10
#20
#30
Remember that the index value of the last element of an array is always one less than the length of the array. Where n
is the length of the array, n - 1
will be the index value of the last item.
Note that you can also access each individual element using negative indexing.
With negative indexing, the last element would have an index of -1
, the second to last element would have an index of -2
, and so on.
Here is how you would get each item in an array using that method:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
#output
#30
#20
#10
You can find out an element's index number by using the index()
method.
You pass the value of the element being searched as the argument to the method, and the element's index number is returned.
import array as arr
numbers = arr.array('i',[10,20,30])
#search for the index of the value 10
print(numbers.index(10))
#output
#0
If there is more than one element with the same value, the index of the first instance of the value will be returned:
import array as arr
numbers = arr.array('i',[10,20,30,10,20,30])
#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))
#output
#0
You've seen how to access each individual element in an array and print it out on its own.
You've also seen how to print the array, using the print()
method. That method gives the following result:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
What if you want to print each value one by one?
This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.
For this you can use a simple for
loop:
import array as arr
numbers = arr.array('i',[10,20,30])
for number in numbers:
print(number)
#output
#10
#20
#30
You could also use the range()
function, and pass the len()
method as its parameter. This would give the same result as above:
import array as arr
values = arr.array('i',[10,20,30])
#prints each individual value in the array
for value in range(len(values)):
print(values[value])
#output
#10
#20
#30
To access a specific range of values inside the array, use the slicing operator, which is a colon :
.
When using the slicing operator and you only include one value, the counting starts from 0
by default. It gets the first item, and goes up to but not including the index number you specify.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 10 and 20 only
print(numbers[:2]) #first to second position
#output
#array('i', [10, 20])
When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 20 and 30 only
print(numbers[1:3]) #second to third position
#output
#rray('i', [20, 30])
Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.
Let's see some of the most commonly used methods which are used for performing operations on arrays.
You can change the value of a specific element by speficying its position and assigning it a new value:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40
print(numbers)
#output
#array('i', [40, 20, 30])
To add one single value at the end of an array, use the append()
method:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40)
print(numbers)
#output
#array('i', [10, 20, 30, 40])
Be aware that the new item you add needs to be the same data type as the rest of the items in the array.
Look what happens when I try to add a float to an array of integers:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40.0)
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
# numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer
But what if you want to add more than one value to the end an array?
Use the extend()
method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets
numbers.extend([40,50,60])
print(numbers)
#output
#array('i', [10, 20, 30, 40, 50, 60])
And what if you don't want to add an item to the end of an array? Use the insert()
method, to add an item at a specific position.
The insert()
function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 in the first position
#remember indexing starts at 0
numbers.insert(0,40)
print(numbers)
#output
#array('i', [40, 10, 20, 30])
To remove an element from an array, use the remove()
method and include the value as an argument to the method.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30])
With remove()
, only the first instance of the value you pass as an argument will be removed.
See what happens when there are more than one identical values:
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
Only the first occurence of 10
is removed.
You can also use the pop()
method, and specify the position of the element to be removed:
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
#remove the first instance of 10
numbers.pop(0)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
And there you have it - you now know the basics of how to create arrays in Python using the array module
. Hopefully you found this guide helpful.
You'll start from the basics and learn in an interacitve and beginner-friendly way. You'll also build five projects at the end to put into practice and help reinforce what you learned.
Thanks for reading and happy coding!
Original article source at https://www.freecodecamp.org
#python
1666082925
This tutorialvideo on 'Arrays in Python' will help you establish a strong hold on all the fundamentals in python programming language. Below are the topics covered in this video:
1:15 What is an array?
2:53 Is python list same as an array?
3:48 How to create arrays in python?
7:19 Accessing array elements
9:59 Basic array operations
- 10:33 Finding the length of an array
- 11:44 Adding Elements
- 15:06 Removing elements
- 18:32 Array concatenation
- 20:59 Slicing
- 23:26 Looping
Python Array Tutorial – Define, Index, Methods
In this article, you'll learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.
The artcile covers arrays that you create by importing the array module
. We won't cover NumPy arrays here.
Let's get started!
Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.
Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.
Lists are one of the most common data structures in Python, and a core part of the language.
Lists and arrays behave similarly.
Just like arrays, lists are an ordered sequence of elements.
They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.
However, lists and arrays are not the same thing.
Lists store items that are of various data types. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.
As mentioned in the section above, arrays store only items that are of the same single data type. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.
Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the array module
in order to be used.
Arrays of the array module
are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.
They are also more compact and take up less memory and space which makes them more size efficient compared to lists.
If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.
In order to create Python arrays, you'll first have to import the array module
which contains all the necassary functions.
There are three ways you can import the array module
:
import array
at the top of the file. This includes the module array
. You would then go on to create an array using array.array()
.import array
#how you would create an array
array.array()
array.array()
all the time, you could use import array as arr
at the top of the file, instead of import array
alone. You would then create an array by typing arr.array()
. The arr
acts as an alias name, with the array constructor then immediately following it.import array as arr
#how you would create an array
arr.array()
from array import *
, with *
importing all the functionalities available. You would then create an array by writing the array()
constructor alone.from array import *
#how you would create an array
array()
Once you've imported the array module
, you can then go on to define a Python array.
The general syntax for creating an array looks like this:
variable_name = array(typecode,[elements])
Let's break it down:
variable_name
would be the name of the array.typecode
specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type.elements
that would be stored in the array, with each element being separated by a comma. You can also create an empty array by just writing variable_name = array(typecode)
alone, without any elements.Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:
TYPECODE | C TYPE | PYTHON TYPE | SIZE |
---|---|---|---|
'b' | signed char | int | 1 |
'B' | unsigned char | int | 1 |
'u' | wchar_t | Unicode character | 2 |
'h' | signed short | int | 2 |
'H' | unsigned short | int | 2 |
'i' | signed int | int | 2 |
'I' | unsigned int | int | 2 |
'l' | signed long | int | 4 |
'L' | unsigned long | int | 4 |
'q' | signed long long | int | 8 |
'Q' | unsigned long long | int | 8 |
'f' | float | float | 4 |
'd' | double | float | 8 |
Tying everything together, here is an example of how you would define an array in Python:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
Let's break it down:
import array as arr
.numbers
array.arr.array()
because of import array as arr
.array()
constructor, we first included i
, for signed integer. Signed integer means that the array can include positive and negative values. Unsigned integer, with H
for example, would mean that no negative values are allowed.Keep in mind that if you tried to include values that were not of i
typecode, meaning they were not integer values, you would get an error:
import array as arr
numbers = arr.array('i',[10.0,20,30])
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
# numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer
In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.
Another way to create an array is the following:
from array import *
#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])
print(numbers)
#output
#array('d', [10.0, 20.0, 30.0])
The example above imported the array module
via from array import *
and created an array numbers
of float data type. This means that it holds only floating point numbers, which is specified with the 'd'
typecode.
To find out the exact number of elements contained in an array, use the built-in len()
method.
It will return the integer number that is equal to the total number of elements in the array you specify.
import array as arr
numbers = arr.array('i',[10,20,30])
print(len(numbers))
#output
# 3
In the example above, the array contained three elements – 10, 20, 30
– so the length of numbers
is 3
.
Each item in an array has a specific address. Individual items are accessed by referencing their index number.
Indexing in Python, and in all programming languages and computing in general, starts at 0
. It is important to remember that counting starts at 0
and not at 1
.
To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.
The general syntax would look something like this:
array_name[index_value_of_item]
Here is how you would access each individual element in an array:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element
#output
#10
#20
#30
Remember that the index value of the last element of an array is always one less than the length of the array. Where n
is the length of the array, n - 1
will be the index value of the last item.
Note that you can also access each individual element using negative indexing.
With negative indexing, the last element would have an index of -1
, the second to last element would have an index of -2
, and so on.
Here is how you would get each item in an array using that method:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
#output
#30
#20
#10
You can find out an element's index number by using the index()
method.
You pass the value of the element being searched as the argument to the method, and the element's index number is returned.
import array as arr
numbers = arr.array('i',[10,20,30])
#search for the index of the value 10
print(numbers.index(10))
#output
#0
If there is more than one element with the same value, the index of the first instance of the value will be returned:
import array as arr
numbers = arr.array('i',[10,20,30,10,20,30])
#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))
#output
#0
You've seen how to access each individual element in an array and print it out on its own.
You've also seen how to print the array, using the print()
method. That method gives the following result:
import array as arr
numbers = arr.array('i',[10,20,30])
print(numbers)
#output
#array('i', [10, 20, 30])
What if you want to print each value one by one?
This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.
For this you can use a simple for
loop:
import array as arr
numbers = arr.array('i',[10,20,30])
for number in numbers:
print(number)
#output
#10
#20
#30
You could also use the range()
function, and pass the len()
method as its parameter. This would give the same result as above:
import array as arr
values = arr.array('i',[10,20,30])
#prints each individual value in the array
for value in range(len(values)):
print(values[value])
#output
#10
#20
#30
To access a specific range of values inside the array, use the slicing operator, which is a colon :
.
When using the slicing operator and you only include one value, the counting starts from 0
by default. It gets the first item, and goes up to but not including the index number you specify.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 10 and 20 only
print(numbers[:2]) #first to second position
#output
#array('i', [10, 20])
When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#get the values 20 and 30 only
print(numbers[1:3]) #second to third position
#output
#rray('i', [20, 30])
Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.
Let's see some of the most commonly used methods which are used for performing operations on arrays.
You can change the value of a specific element by speficying its position and assigning it a new value:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40
print(numbers)
#output
#array('i', [40, 20, 30])
To add one single value at the end of an array, use the append()
method:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40)
print(numbers)
#output
#array('i', [10, 20, 30, 40])
Be aware that the new item you add needs to be the same data type as the rest of the items in the array.
Look what happens when I try to add a float to an array of integers:
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 to the end of numbers
numbers.append(40.0)
print(numbers)
#output
#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
# numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer
But what if you want to add more than one value to the end an array?
Use the extend()
method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets
numbers.extend([40,50,60])
print(numbers)
#output
#array('i', [10, 20, 30, 40, 50, 60])
And what if you don't want to add an item to the end of an array? Use the insert()
method, to add an item at a specific position.
The insert()
function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
#add the integer 40 in the first position
#remember indexing starts at 0
numbers.insert(0,40)
print(numbers)
#output
#array('i', [40, 10, 20, 30])
To remove an element from an array, use the remove()
method and include the value as an argument to the method.
import array as arr
#original array
numbers = arr.array('i',[10,20,30])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30])
With remove()
, only the first instance of the value you pass as an argument will be removed.
See what happens when there are more than one identical values:
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
numbers.remove(10)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
Only the first occurence of 10
is removed.
You can also use the pop()
method, and specify the position of the element to be removed:
import array as arr
#original array
numbers = arr.array('i',[10,20,30,10,20])
#remove the first instance of 10
numbers.pop(0)
print(numbers)
#output
#array('i', [20, 30, 10, 20])
And there you have it - you now know the basics of how to create arrays in Python using the array module
. Hopefully you found this guide helpful.
Thanks for reading and happy coding!
#python #programming
1624531051
Alerts4Dynamics is productivity app for Dynamics 365 CRM that helps to create, schedule, manage and track alerts. It helps to notify and pass relevant information to target audience right within Dynamics 365 CRM. These notifications can be created and displayed indefinitely or for a defined scheduled period. Notification button is available on all entities and can be accessed from anywhere in the CRM.
Features
• Create Announcement and Rule Based/Record Based alerts.
• Alerts can be sent as Pop-ups, Form Notifications or Email to target Dynamics 365 CRM users.
• Categorize alerts as Information, Warning or Critical.
• Track log of read/dismissed alerts by users.
• Define process start date from when the notifications will start getting created and process end date when creation of new notifications will stop. Also, add the display end date for notification.
#dynamics 365 pop-up alert #dynamics 365 email alerts #dynamics 365 bulk alerts #dynamics crm pop-up alert #dynamics 365 notifications #dynamics crm alert
1625057623
Click2Undo is a productivity app that helps you to undo changes in the data in Dynamics 365 CRM with a single click. Be it the last change that you’d want to restore, or the changes that were done in the past which you would like to get back, Click2Undo can do it without any hassle. This provides a safety net within which users can conduct day-to-day activities without fear of losing data due to human or technical errors.
Click2Undo is available for Dynamics CRM 8.2 and above, Dataverse (Power Apps). It supports deployment models - On-Premises and Online.
Features
• Entity Support: Click2Undo provides support to all OOB as well as Custom Entities
• Undo Last Changes: Ability to restore the last changes done to a Dynamics 365 CRM record by clicking the Click2Undo button
• Undo Past Changes: Ability to undo past changes made to multiple fields on Dynamics 365 CRM records in one go using History button
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#restore last state of dynamics 365 records #restoring deleted dynamics 365 records #recovering deleted dynamics 365 records #recover deleted dynamics crm records #dynamics 365 online recover deleted records #restore records dynamics crm
1599278730
We all know about the basic data structure, which is** Array **pretty well. And in java they are static. It means we have to allocate memory for the array ahead of time. The memory will define the number of elements that the array can hold. But what if we have know idea about the exact number of elements that we are going to insert before hand. Then the best thing is to have a dynamic array.
A dynamic array automatically grows when we try to make an insertion and there is no space left for the new item. A simple dynamic array can be constructed, by using an array of fixed-size. The elements of the array are stored contiguously, for an instance, if it is an integer type array it will take 4 bytes of space per integer element. The remaining positions towards the end are reserved and unused. New elements can be added to the end of the array until the reserved space is fully utilized. If you still need to add up more elements even after that, the array needs to be resized which is a very expensive task. Usually it doubles its size.
Following is the Figure 1, where you can find the Array class, to model a dynamic behavior by using a static array in Java. Basic array operations are implemented below.
public class Array {
private int[] items;
private int count;
public Array(int length) {
items = new int[length];
}
public void print() {
for(int i=0;i<count;i++) {
System.out.println(items[i]);
}
}
public void insert(int number) {
//If an item is added to the end
items[count]=number;
count++;
//If the array is full, resize it
if(items.length == count) {
int[] newItems = new int[count*2];
for(int i=0;i<count;i++) {
newItems[i]=items[i];
}
items=newItems;
}
}
//Delete
public void removeAt(int index) {
if(index<0 || index>=count ) {
throw new IllegalArgumentException();
}
for(int i=index;i<count;i++) {
items[i]=items[i+1];
}
count--;
}
//Search
public int indexOf(int number) {
for(int i=0;i<count;i++) {
if(number == items[i]) {
return i;
}
}
return -1;
}
}
#dynamic-array #data-structures #java #arrays