A Review of Basic Algorithms and Data Structures in Python: Graph Algorithms

A Review of Basic Algorithms and Data Structures in Python: Graph Algorithms

<strong>Originally published by </strong><a href="https://medium.com/@diogoribeiro_94486" target="_blank">Diogo Ribeiro</a> <em>at&nbsp;</em><a href="https://medium.com/@diogoribeiro_94486/a-review-of-basic-algorithms-and-data-structures-in-python-graph-algorithms-d73691d86211" target="_blank"><em>Medium</em></a>

Introduction

Recently, while reviewing basic graph algorithms, I decided to write down my study notes as an article in case someone else finds them useful. To verify my understanding, I wrote minimal implementations of the algorithms in Python which make up the bulk of this article. Simple unit tests accompany the code. The unit tests can also be used as examples of using the code.

I’m hoping to write at least a few follow-up posts, focusing on combinatorial algorithms, string algorithms, and maybe even one on computational geometry.

Most of the code was written to be easy to understand without having to reference much else (with a few exceptions, for example, Kruskal’s algorithm uses the disjoint set structure defined in another section). This results in some duplication, especially in the unit tests. I consider this to be acceptable, given that the purpose of the code is to be used as educational material and not as code in production use that needs a day to day maintenance.

One last thing before we start: I wrote the article and all the code relatively quickly. Mistakes and bugs are definitely possible. Corrections are appreciated; please comment below if you find any.

Table Of Contents

Algorithms and data structures in this article:

  • Disjoint Set (Union-Find)
  • Kruskal’s Minimum Spanning Tree (MST)
  • Depth First Search (DFS)
  • Breadth First Search (BFS)
  • Kahn’s Topological Sort Algorithm
  • Dijkstra’s Shortest Path Algorithm
  • Bellman-Ford Shortest Path Algorithm

Disjoint Set (Union-Find)

The disjoint set structure is used to keep track of a partitioning of a set of objects into subsets. The main question it needs to answer is “do X and Y belong to the same subset?” and the main operation it needs to support is joining two subsets so that elements in either of the subsets will belong to the same larger subset afterward.

Quick and minimal implementation is provided below. The implementation below uses a forest to keep track of the subsets in the partition. Each tree in the forest is one subset, and the root of the tree is the “representative” element of the subset. To check if two elements belong to the same subset, we check if they have the same representative element.

Noting that the ideal tree in this implementation is a star (this minimizes the number of recursive find calls), we "compress" the paths on each call to find. That is, we set the parent of all the elements on the path to the representative to the representative as we unwind down the recursive call stack.

class DisjointSet(object):
  def __init__(self, n):
    """
    Initializes a disjoint set structure consisting of n disjoint sets.
    """
    self.parent = list(range(n))
  def find(self, x):
    """Returns the representative element of the set x belongs to."""
    if self.parent[x] != x:
      self.parent[x] = self.find(self.parent[x])
    return self.parent[x]
  def union(self, x, y):
    """Joins the sets containing x and y."""
    self.parent[self.find(x)] = self.find(y)

And the accompanied unit test:

import unittest
from union_find import DisjointSet

class DisjointSetTest(unittest.TestCase):
  def test_initialized_state(self):
    d = DisjointSet(3)
    self.assertEqual(d.find(0), 0)
    self.assertEqual(d.find(1), 1)
    self.assertEqual(d.find(2), 2)
  def test_basic_union(self):
    d = DisjointSet(3)
    d.union(0, 1)
    self.assertEqual(d.find(0), d.find(1))
    self.assertNotEqual(d.find(1), d.find(2))
  def test_basic_union_idempotent(self):
    d = DisjointSet(2)
    d.union(0, 1)
    d.union(0, 1)
    self.assertEqual(d.find(0), d.find(1))
  def test_union_all(self):
    d = DisjointSet(100)
    for i in range(1, 100):
      d.union(i - 1, i)
    for i in range(1, 100):
      self.assertEqual(d.find(0), d.find(i))

Kruskal’s Minimum Spanning Tree (MST)

Kruskal’s minimum spanning tree algorithm is a good example of a greedy algorithm. Starting with a forest consisting of individual disjoint vertices, at each step we pick the next best edge (one with minimal weight) provided it does not introduce a cycle into the forest, and continue until the forest becomes a tree. It’s rather easy to prove that the resulting tree is a minimum spanning tree.

Using the disjoint set structure shown above to keep track of the minimum spanning forest, the implementation below is very simple:

from collections import namedtuple
from union_find import DisjointSet

# Putting weight as the first element means Edges will sort by weight first,
# then source and target (lexicographically).
Edge = namedtuple('Edge', ['weight', 'source', 'target'])

def kruskal_mst(n, edges):
  """
  Given a positive integer n (number of vertices) and a collection of Edge
  namedtuple objects representing the undirected edges of a graph, returns a
  list of edges forming a minimal spanning tree of the graph. Assumes the
  vertices are numbers in the range 0 to n - 1.  Also assumes input is a
  valid connected undirected graph and that for two vertices v and w only one
  of (v, w) or (w, v) is an edge in the input. Output is undefined if these
  assumptions are not satisfied.
  """
  d = DisjointSet(n)
  mst_tree = []
  for edge in sorted(edges):
    if d.find(edge.source) != d.find(edge.target):
      mst_tree.append(edge)
      if len(mst_tree) == n - 1:
        break
      d.union(edge.source, edge.target)
  return mst_tree

And the accompanied unit test:

import unittest
from kruskal import kruskal_mst, Edge

class KruskalMSPTest(unittest.TestCase):
  def test_single_vertex_graph(self):
    self.assertEqual(kruskal_mst(1, []), [])
  def test_single_edge_graph(self):
    edges = [Edge(source=0, target=1, weight=10)]
    self.assertEqual(kruskal_mst(2, edges), edges)
  def test_cycle_5(self):
    edges = [
      Edge(source=0, target=1, weight=50),
      Edge(source=1, target=2, weight=30),
      Edge(source=2, target=3, weight=60),
      Edge(source=3, target=4, weight=20),
      Edge(source=4, target=0, weight=10),
    ]
    # Everything except the heaviest edge. Output sorted by weight.
    self.assertEqual(kruskal_mst(5, edges), [
      Edge(source=4, target=0, weight=10),
      Edge(source=3, target=4, weight=20),
      Edge(source=1, target=2, weight=30),
      Edge(source=0, target=1, weight=50),
    ])
  def test_complete_graph_4(self):
    edges = [
      Edge(source=0, target=1, weight=10),
      Edge(source=0, target=2, weight=30),
      Edge(source=0, target=3, weight=40),
      Edge(source=1, target=2, weight=20),
      Edge(source=1, target=3, weight=50),
      Edge(source=2, target=3, weight=60),
    ]
    self.assertEqual(kruskal_mst(4, edges), [
      Edge(source=0, target=1, weight=10),
      Edge(source=1, target=2, weight=20),
      Edge(source=0, target=3, weight=40),
    ])

Depth First Search (DFS)

Depth-first search is arguably the simplest graph traversal algorithm. It’s a simple recursive algorithm that just needs to keep track of which vertices have already been processed. In fact, many other recursive algorithms can be thought of as a DFS on some underlying graph (e.g. binary search is guided DFS on the binary search tree). DFS can be used to determine if there is a path from a vertex to another and to visit every vertex starting from a source vertex. Variations of DFS can be used for determining connected components and doing topological sorting. The code below simply uses DFS to return all vertices reachable from a starting vertex.

def dfs(graph, source):
  """
  Given a directed graph (format described below), and a source vertex,
  returns a set of vertices reachable from source.
  The graph parameter is expected to be a dictionary mapping each vertex to a
  list of vertices indicating outgoing edges. For example if vertex v has
  outgoing edges to u and w we have graph[v] = [u, w].
  """
  visited = set()
  def _recurse(v):
    if v in visited:
      return
    visited.add(v)
    for w in graph[v]:
      _recurse(w)
  _recurse(source)
  return visited

And the accompanied unit test:

import unittest
from dfs import dfs

class DFSTest(unittest.TestCase):
  def test_single_vertex(self):
    graph = {0: []}
    self.assertEqual(dfs(graph, 0), {0})
  def test_single_vertex_with_loop(self):
    graph = {0: [0]}
    self.assertEqual(dfs(graph, 0), {0})
  def test_two_vertices_no_path(self):
    graph = {
      0: [],
      1: [],
    }
    self.assertEqual(dfs(graph, 0), {0})
    self.assertEqual(dfs(graph, 1), {1})
  def test_two_vertices_with_simple_path(self):
    graph = {
      0: [1],
      1: [],
    }
    self.assertEqual(dfs(graph, 0), {0, 1})
    self.assertEqual(dfs(graph, 1), {1})
  def test_complete_graph(self):
    def _complete_graph(n):
      return {v: list(set(range(n)) - {v}) for v in range(n)}
    for n in range(2, 10):
      graph = _complete_graph(n)
      for v in range(n):
        self.assertEqual(dfs(graph, v), set(range(n)))
  def test_cycle_5(self):
    graph = {
      0: [1],
      1: [2],
      2: [3],
      3: [4],
      4: [0],
    }
    for v in range(5):
      self.assertEqual(dfs(graph, v), {0, 1, 2, 3, 4})

Breadth First Search (BFS)

BFS is one of the simplest graph algorithms and a good algorithm to understand prior to Dijkstra’s, which is coming up next. It can be used to simply traverse a graph and visit every vertex, to search for a particular vertex, or find the shortest path (assuming edges don’t have weights) to every vertex starting from a single vertex.

from collections import deque

def bfs(graph, source, target):
  """
  Given a directed graph (format described below), and source and target
  vertices, returns a shortest unweighted path as a list of vertices going
  from source to target, or None if no such path exists. Returned path will
  not include the source vertex in it.
  The graph parameter is expected to be a dictionary mapping each vertex to a
  list of vertices indicating outgoing edges. For example if vertex v has
  outgoing edges to u and w we have graph[v] = [u, w].
  """
  q = deque([source])
  # previous_vertex[v] holds the immediate vertex before v in the shortest
  # path from source to v. This dictionary also acts as our "visited" set
  # since we set previous_vertex[v] as soon as the vertex enters our queue.
  previous_vertex = {source: source}
  while q:
    v = q.popleft()
    if v == target:
      return _construct_path(previous_vertex, source, target)
    for w in graph[v]:
      if w not in previous_vertex:
        previous_vertex[w] = v
        q.append(w)
  return None

def _construct_path(previous_vertex, source, target):
  if source == target:
    return []
  return _construct_path(previous_vertex, source,
               previous_vertex[target]) + [target]

And the accompanied unit test:

import unittest
from bfs import bfs

class BFSTest(unittest.TestCase):
  def test_single_vertex(self):
    graph = {0: []}
    self.assertEqual(bfs(graph, 0, 0), [])
  def test_single_vertex_with_loop(self):
    graph = {0: [0]}
    self.assertEqual(bfs(graph, 0, 0), [])
  def test_two_vertices_no_path(self):
    graph = {
      0: [],
      1: [],
    }
    self.assertEqual(bfs(graph, 0, 1), None)
  def test_two_vertices_with_simple_path(self):
    graph = {
      0: [1],
      1: [],
    }
    self.assertEqual(bfs(graph, 0, 1), [1])
  def test_complete_graph(self):
    def _complete_graph(n):
      return {v: list(set(range(n)) - {v}) for v in range(n)}
    for n in range(2, 10):
      graph = _complete_graph(n)
      for v in range(n):
        for w in range(n):
          self.assertEqual(bfs(graph, v, w),
                   [] if v == w else [w])
  def test_cycle_5(self):
    graph = {
      0: [4, 1],
      1: [0, 2],
      2: [1, 3],
      3: [2, 4],
      4: [3, 0],
    }
    self.assertEqual(bfs(graph, 0, 2), [1, 2])
    self.assertEqual(bfs(graph, 0, 3), [4, 3])

Kahn’s Topological Sort Algorithm

Given a directed acyclic graph (DAG) representing a set of, say, tasks and their dependencies, the topological sort is the problem of finding an order of task execution that will satisfy all the dependencies. This problem arises in a variety of applications. Examples include task scheduling, build systems (e.g. Bazel), parallel pipelines (e.g. Hadoop), and formula evaluation (e.g. in spreadsheets).

While a variation of DFS can be used for topological sorting, my personal favorite algorithm for doing topological sorts is Kahn’s algorithm, due to its intuitiveness. The idea behind the algorithm is simple: start with vertices with no incoming edges, process them, and then remove them and all their outgoing edges from the graph and continue until there’s nothing left in the graph.

In the code below, instead of returning a particular topological sort, the algorithm assigns a “sequence” to each vertex, such that if sequence[v] < sequence[w] then v should be before w in any topological sort of the graph. This simplifies unit testing, and also allows for easier use of the output in cases where parallelization is possible (since all tasks with the same sequence number can be executed in parallel).

from collections import deque, namedtuple
Vertex = namedtuple('Vertex', ['name', 'incoming', 'outgoing'])

def build_doubly_linked_graph(graph):
  """
  Given a graph with only outgoing edges, build a graph with incoming and
  outgoing edges. The returned graph will be a dictionary mapping vertex to a
  Vertex namedtuple with sets of incoming and outgoing vertices.
  """
  g = {v:Vertex(name=v, incoming=set(), outgoing=set(o))
     for v, o in graph.items()}
  for v in g.values():
    for w in v.outgoing:
      if w in g:
        g[w].incoming.add(v.name)
      else:
        g[w] = Vertex(name=w, incoming={v}, outgoing=set())
  return g

def kahn_top_sort(graph):
  """
  Given an acyclic directed graph (format described below), returns a
  dictionary mapping vertex to sequence such that sorting by the sequence
  component will result in a topological sort of the input graph. Output is
  undefined if input is a not a valid DAG.
  The graph parameter is expected to be a dictionary mapping each vertex to a
  list of vertices indicating outgoing edges. For example if vertex v has
  outgoing edges to u and w we have graph[v] = [u, w].
  """
  g = build_doubly_linked_graph(graph)
  # sequence[v] < sequence[w] implies v should be before w in the topological
  # sort.
  q = deque(v.name for v in g.values() if not v.incoming)
  sequence = {v: 0 for v in q}
  while q:
    v = q.popleft()
    for w in g[v].outgoing:
      g[w].incoming.remove(v)
      if not g[w].incoming:
        sequence[w] = sequence[v] + 1
        q.append(w)
  return sequence

And the accompanied unit test:

import unittest
from kahn import kahn_top_sort

class KahnTopSortTest(unittest.TestCase):
  def test_single_vertex(self):
    graph = {
      0: [],
    }
    self.assertEqual(kahn_top_sort(graph), {
      0: 0,
    })
  def test_total_order_2(self):
    graph = {
      0: [1],
      1: [],
    }
    self.assertEqual(kahn_top_sort(graph), {
      0: 0,
      1: 1,
    })
  def test_total_order_3(self):
    graph = {
      0: [1],
      1: [2],
      2: [],
    }
    self.assertEqual(kahn_top_sort(graph), {
      0: 0,
      1: 1,
      2: 2,
    })
  def test_two_independent_total_orders(self):
    # 0 -> 1 -> 2
    # 3 -> 4 -> 5
    graph = {
      0: [1],
      1: [2],
      2: [],
      3: [4],
      4: [5],
      5: [],
    }
    self.assertEqual(kahn_top_sort(graph), {
      0: 0,
      3: 0,
      1: 1,
      4: 1,
      2: 2,
      5: 2,
    })
  def test_simple_dag_1(self):
    # 0 -> 1 -> 2
    #   \ /
    #  3
    graph = {
      0: [1, 3],
      1: [2],
      2: [],
      3: [1],
    }
    self.assertEqual(kahn_top_sort(graph), {
      0: 0,
      3: 1,
      1: 2,
      2: 3,
    })

Dijkstra’s Shortest Path Algorithm

Dijkstra’s shortest path algorithm is very similar to BFS, except a priority queue is used instead of a regular queue. A proper implementation would use a priority queue with an “update key” operation which would reduce the redundant items in the queue. The implementation below, for the sake of simplicity, uses the built-in Python PriorityQueue which does not support "update key".

The invariant in the algorithm is that each time we get an item from the queue, we know that we have the shortest path from source to it already (this is where the guarantee of non-negative weights is key, as this invariant can fail if we have negative weights.)

from collections import namedtuple, defaultdict
from Queue import PriorityQueue
Edge = namedtuple('Edge', ['target', 'weight'])

def dijkstra(graph, source, target):
  """
  Given a directed graph (format described below), and source and target
  vertices, returns a shortest path as a list of vertices going from source
  to target, along with the distance of the shortest path, or None if no such
  path exists. Returned path will not include the source vertex in it.
  Assumes non-negative weights.
  The graph parameter is expected to be a dictionary mapping each vertex to a
  list of Edge named tuples indicating the vertex's outgoing edges. For
  example if vertex v has outgoing edges to u and w with weights 10 and 20
  respectively, we have graph[v] = [Edge(u, 10), Edge(w, 20)].
  """
  q = PriorityQueue()
  q.put((0, source))
  # previous_vertex[v] holds the immediate vertex before v in the shortest
  # path from source to v. This dictionary also acts as our "visited" set
  # since we set previous_vertex[v] as soon as the vertex enters our queue.
  previous_vertex = {source: source}
  # Arguably not the best way to represent infinity but it works for the sake
  # of learning the algorithm.
  shortest_distance = defaultdict(lambda: float('inf'))
  shortest_distance[source] = 0
  while not q.empty():
    (distance, v) = q.get()
    if v == target:
      return (distance, _construct_path(previous_vertex, source, target))
    for edge in graph[v]:
      alt_distance = edge.weight + distance
      if alt_distance < shortest_distance[edge.target]:
        shortest_distance[edge.target] = alt_distance
        q.put((alt_distance, edge.target))
        previous_vertex[edge.target] = v
  return None

def _construct_path(previous_vertex, source, target):
  if source == target:
    return []
  return _construct_path(previous_vertex, source,
               previous_vertex[target]) + [target]

And the accompanied unit test:

import unittest
from dijkstra import dijkstra, Edge

class DijkstraTest(unittest.TestCase):
  def test_single_vertex(self):
    graph = {0: []}
    self.assertEqual(dijkstra(graph, 0, 0), (0, []))
  def test_two_vertices_no_path(self):
    graph = {
      0: [],
      1: [],
    }
    self.assertEqual(dijkstra(graph, 0, 1), None)
  def test_two_vertices_with_path(self):
    graph = {
      0: [Edge(target=1, weight=10)],
      1: [],
    }
    self.assertEqual(dijkstra(graph, 0, 1), (10, [1]))
  def test_cycle_3(self):
    graph = {
      0: [Edge(target=1, weight=10), Edge(target=2, weight=30)],
      1: [Edge(target=0, weight=10), Edge(target=2, weight=10)],
      2: [Edge(target=0, weight=30), Edge(target=1, weight=30)],
    }
    self.assertEqual(dijkstra(graph, 0, 2), (20, [1, 2]))
  def test_clrs_example(self):
    graph = {
      's': [
        Edge(target='t', weight=3),
        Edge(target='y', weight=5),
      ],
      't': [
        Edge(target='x', weight=6),
        Edge(target='y', weight=2),
      ],
      'y': [
        Edge(target='t', weight=1),
        Edge(target='z', weight=6),
      ],
      'x': [
        Edge(target='z', weight=2),
      ],
      'z': [
        Edge(target='x', weight=7),
        Edge(target='s', weight=3),
      ],
    }
    distance, path = dijkstra(graph, 's', 'z')
    self.assertEqual(distance, 11)
    self.assertIn(path, [
      ['y', 'z'],
      ['t', 'y', 'x', 'z'],
    ])
    distance, path = dijkstra(graph, 's', 'x')
    self.assertEqual(distance, 9)
    self.assertIn(path, [
      ['t', 'x'],
      ['y', 'x'],
    ])

Bellman-Ford Shortest Path Algorithm

Bellman-Ford is another single-source shortest path algorithm. It’s very easy to implement but has worse running time than Dijkstra’s. While in Dijkstra’s we relax edges greedily based on the next closest vertex to the source, in Bellman-Ford we relax every edge exactly n-1 times. Each such iteration guarantees to increase the number of vertices for which we have the shortest path by at least one, and hence after n-1 iterations, we have the shortest path to every vertex. We then do a final loop over all the edges and try to relax further. If we succeed, we know a negative cycle exists. This is the key advantage of Bellman-Ford as compared to Dijkstra’s (Dijkstra’s algorithm does not work if negative weights exist.)

Here’s a basic implementation:

from collections import namedtuple, defaultdict
Edge = namedtuple('Edge', ['target', 'weight'])

def bellman_ford(graph, source, target):
  """
  Given a directed graph (format described below), and source and target
  vertices, returns a shortest path as a list of vertices going from source
  to target, along with the distance of the shortest path, or None if no such
  path exists and -1 if a negative loop is found. Returned path will not
  include the source vertex in it. Assumes non-negative weights.
  The graph parameter is expected to be a dictionary mapping each vertex to a
  list of Edge named tuples indicating the vertex's outgoing edges. For
  example if vertex v has outgoing edges to u and w with weights 10 and 20
  respectively, we have graph[v] = [Edge(u, 10), Edge(w, 20)].
  """
  # previous_vertex[v] holds the immediate vertex before v in the shortest
  # path from source to v. This dictionary also acts as our "visited" set
  # since we set previous_vertex[v] as soon as the vertex enters our queue.
  previous_vertex = {source: source}
  # Arguably not the best way to represent infinity but it works for the sake
  # of learning the algorithm.
  shortest_distance = defaultdict(lambda: float('inf'))
  shortest_distance[source] = 0
  # Run n - 1 times. We start by knowing the shortest path to 1 vertex
  # (source itself) and each iteration below increases the vertices for which
  # we have the shortest path to by one. This means at the end we have the
  # shortest path to 1 + (n - 1) = n vertices.
  for i in range(len(graph) - 1):
    for v in graph:
      for edge in graph[v]:
        alt_distance = shortest_distance[v] + edge.weight
        if alt_distance < shortest_distance[edge.target]:
          shortest_distance[edge.target] = alt_distance
          previous_vertex[edge.target] = v
  # Final loop over all edges to check for negative loops. If at this point
  # we find a shorter alternative path it means a negative loop exists.
  for v in graph:
    for edge in graph[v]:
      alt_distance = shortest_distance[v] + edge.weight
      if alt_distance < shortest_distance[edge.target]:
        return -1
  if shortest_distance[target] < float('inf'):
    return (shortest_distance[target],
        _construct_path(previous_vertex, source, target))
  return None

def _construct_path(previous_vertex, source, target):
  if source == target:
    return []
  return _construct_path(previous_vertex, source,
               previous_vertex[target]) + [target]

And as before, accompanied unit test, which is a copy of the one used for Dijkstra’s, with an additional test for negative cycles:

import unittest
from bellman import bellman_ford, Edge

class BellmanFordTest(unittest.TestCase):
  def test_single_vertex(self):
    graph = {0: []}
    self.assertEqual(bellman_ford(graph, 0, 0), (0, []))
  def test_two_vertices_no_path(self):
    graph = {
      0: [],
      1: [],
    }
    self.assertEqual(bellman_ford(graph, 0, 1), None)
  def test_two_vertices_with_path(self):
    graph = {
      0: [Edge(target=1, weight=10)],
      1: [],
    }
    self.assertEqual(bellman_ford(graph, 0, 1), (10, [1]))
  def test_cycle_3(self):
    graph = {
      0: [Edge(target=1, weight=10), Edge(target=2, weight=30)],
      1: [Edge(target=0, weight=10), Edge(target=2, weight=10)],
      2: [Edge(target=0, weight=30), Edge(target=1, weight=30)],
    }
    self.assertEqual(bellman_ford(graph, 0, 2), (20, [1, 2]))
  def test_negative_cycle_3(self):
    graph = {
      0: [Edge(target=1, weight=10), Edge(target=2, weight=30)],
      1: [Edge(target=0, weight=10), Edge(target=2, weight=10)],
      2: [Edge(target=0, weight=-30), Edge(target=1, weight=30)],
    }
    self.assertEqual(bellman_ford(graph, 0, 2), -1)
  def test_clrs_example(self):
    graph = {
      's': [
        Edge(target='t', weight=3),
        Edge(target='y', weight=5),
      ],
      't': [
        Edge(target='x', weight=6),
        Edge(target='y', weight=2),
      ],
      'y': [
        Edge(target='t', weight=1),
        Edge(target='z', weight=6),
      ],
      'x': [
        Edge(target='z', weight=2),
      ],
      'z': [
        Edge(target='x', weight=7),
        Edge(target='s', weight=3),
      ],
    }
    distance, path = bellman_ford(graph, 's', 'z')
    self.assertEqual(distance, 11)
    self.assertIn(path, [
      ['y', 'z'],
      ['t', 'y', 'x', 'z'],
    ])
    distance, path = bellman_ford(graph, 's', 'x')
    self.assertEqual(distance, 9)
    self.assertIn(path, [
      ['t', 'x'],
      ['y', 'x'],
    ])

Python GUI Programming Projects using Tkinter and Python 3

Python GUI Programming Projects using Tkinter and Python 3

Python GUI Programming Projects using Tkinter and Python 3

Description
Learn Hands-On Python Programming By Creating Projects, GUIs and Graphics

Python is a dynamic modern object -oriented programming language
It is easy to learn and can be used to do a lot of things both big and small
Python is what is referred to as a high level language
Python is used in the industry for things like embedded software, web development, desktop applications, and even mobile apps!
SQL-Lite allows your applications to become even more powerful by storing, retrieving, and filtering through large data sets easily
If you want to learn to code, Python GUIs are the best way to start!

I designed this programming course to be easily understood by absolute beginners and young people. We start with basic Python programming concepts. Reinforce the same by developing Project and GUIs.

Why Python?

The Python coding language integrates well with other platforms – and runs on virtually all modern devices. If you’re new to coding, you can easily learn the basics in this fast and powerful coding environment. If you have experience with other computer languages, you’ll find Python simple and straightforward. This OSI-approved open-source language allows free use and distribution – even commercial distribution.

When and how do I start a career as a Python programmer?

In an independent third party survey, it has been revealed that the Python programming language is currently the most popular language for data scientists worldwide. This claim is substantiated by the Institute of Electrical and Electronic Engineers, which tracks programming languages by popularity. According to them, Python is the second most popular programming language this year for development on the web after Java.

Python Job Profiles
Software Engineer
Research Analyst
Data Analyst
Data Scientist
Software Developer
Python Salary

The median total pay for Python jobs in California, United States is $74,410, for a professional with one year of experience
Below are graphs depicting average Python salary by city
The first chart depicts average salary for a Python professional with one year of experience and the second chart depicts the average salaries by years of experience
Who Uses Python?

This course gives you a solid set of skills in one of today’s top programming languages. Today’s biggest companies (and smartest startups) use Python, including Google, Facebook, Instagram, Amazon, IBM, and NASA. Python is increasingly being used for scientific computations and data analysis
Take this course today and learn the skills you need to rub shoulders with today’s tech industry giants. Have fun, create and control intriguing and interactive Python GUIs, and enjoy a bright future! Best of Luck
Who is the target audience?

Anyone who wants to learn to code
For Complete Programming Beginners
For People New to Python
This course was designed for students with little to no programming experience
People interested in building Projects
Anyone looking to start with Python GUI development
Basic knowledge
Access to a computer
Download Python (FREE)
Should have an interest in programming
Interest in learning Python programming
Install Python 3.6 on your computer
What will you learn
Build Python Graphical User Interfaces(GUI) with Tkinter
Be able to use the in-built Python modules for their own projects
Use programming fundamentals to build a calculator
Use advanced Python concepts to code
Build Your GUI in Python programming
Use programming fundamentals to build a Project
Signup Login & Registration Programs
Quizzes
Assignments
Job Interview Preparation Questions
& Much More

Guide to Python Programming Language

Guide to Python Programming Language

Guide to Python Programming Language

Description
The course will lead you from beginning level to advance in Python Programming Language. You do not need any prior knowledge on Python or any programming language or even programming to join the course and become an expert on the topic.

The course is begin continuously developing by adding lectures regularly.

Please see the Promo and free sample video to get to know more.

Hope you will enjoy it.

Basic knowledge
An Enthusiast Mind
A Computer
Basic Knowledge To Use Computer
Internet Connection
What will you learn
Will Be Expert On Python Programming Language
Build Application On Python Programming Language

Python Programming Tutorials For Beginners

Python Programming Tutorials For Beginners

Python Programming Tutorials For Beginners

Description
Hello and welcome to brand new series of wiredwiki. In this series i will teach you guys all you need to know about python. This series is designed for beginners but that doesn't means that i will not talk about the advanced stuff as well.

As you may all know by now that my approach of teaching is very simple and straightforward.In this series i will be talking about the all the things you need to know to jump start you python programming skills. This series is designed for noobs who are totally new to programming, so if you don't know any thing about

programming than this is the way to go guys Here is the links to all the videos that i will upload in this whole series.

In this video i will talk about all the basic introduction you need to know about python, which python version to choose, how to install python, how to get around with the interface, how to code your first program. Than we will talk about operators, expressions, numbers, strings, boo leans, lists, dictionaries, tuples and than inputs in python. With

Lots of exercises and more fun stuff, let's get started.

Download free Exercise files.

Dropbox: https://bit.ly/2AW7FYF

Who is the target audience?

First time Python programmers
Students and Teachers
IT pros who want to learn to code
Aspiring data scientists who want to add Python to their tool arsenal
Basic knowledge
Students should be comfortable working in the PC or Mac operating system
What will you learn
know basic programming concept and skill
build 6 text-based application using python
be able to learn other programming languages
be able to build sophisticated system using python in the future

To know more: