# Python: Sort a list of elements using Topological sort

## Python Search and Sorting : Exercise-22 with Solution

Write a Python program to sort a list of elements using Topological sort.

**Sample Solution**:

**Python Code:**

```
# License https://bit.ly/2InTS3W
# a
# / \
# b c
# / \
# d e
edges = {'a': ['c', 'b'], 'b': ['d', 'e'], 'c': [], 'd': [], 'e': []}
vertices = ['a', 'b', 'c', 'd', 'e']
def topological_sort(start, visited, sort):
"""Perform topolical sort on a directed acyclic graph."""
current = start
# add current to visited
visited.append(current)
neighbors = edges[current]
for neighbor in neighbors:
# if neighbor not in visited, visit
if neighbor not in visited:
sort = topological_sort(neighbor, visited, sort)
# if all neighbors visited add current to sort
sort.append(current)
# if all vertices haven't been visited select a new one to visit
if len(visited) != len(vertices):
for vertice in vertices:
if vertice not in visited:
sort = topological_sort(vertice, visited, sort)
# return sort
return sort
sort = topological_sort('a', [], [])
print(sort)
```

Sample Output:

['c', 'd', 'e', 'b', 'a']

**Flowchart: **

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**Next:** Write a Python program to sort a list of elements using Tree sort.

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## Python: Tips of the Day

**The Zip() Function:**

>>> students = ('John', 'Mary', 'Mike') >>> ages = (15, 17, 16) >>> scores = (90, 88, 82, 17, 14) >>> for student, age, score in zip(students, ages, scores): ... print(f'{student}, age: {age}, score: {score}') ... John, age: 15, score: 90 Mary, age: 17, score: 88 Mike, age: 16, score: 82 >>> zipped = zip(students, ages, scores) >>> a, b, c = zip(*zipped) >>> print(b) (15, 17, 16)

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