Conditions

Python supports the usual logical conditions from mathematics:

  • Equals: a == b

  • Not Equals: a != b

  • Less than: a < b

  • Less than or equal to: a <= b

  • Greater than: a > b

  • Greater than or equal to: a >= b

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 33
 5    b = 200
 6    if b > a:
 7        print("b is greater than a")
 8
 9
10if __name__ == "__main__":
11    main()

Indentation

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 33
 5    b = 200
 6    if b > a:
 7    print("b is greater than a") # you will get an error
 8
 9
10if __name__ == "__main__":
11    main()

if-then-elif

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 33
 5    b = 33
 6    if b > a:
 7        print("b is greater than a")
 8    elif a == b:
 9        print("a and b are equal")
10
11
12if __name__ == "__main__":
13    main()

if-then-else

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 200
 5    b = 33
 6    if b > a:
 7        print("b is greater than a")
 8    else:
 9        print("b is not greater than a")
10
11
12if __name__ == "__main__":
13    main()

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 200
 5    b = 33
 6    if b > a:
 7        print("b is greater than a")
 8    elif a == b:
 9        print("a and b are equal")
10    else:
11        print("a is greater than b")
12
13
14if __name__ == "__main__":
15    main()

Nested if-then-else

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    x = 41
 5    if x > 10:
 6        print("Above ten,")
 7    if x > 20:
 8        print("and also above 20!")
 9    else:
10        print("but not above 20.")
11
12
13if __name__ == "__main__":
14    main()

Logical operators

And

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 200
 5    b = 33
 6    c = 500
 7    if a > b and c > a:
 8        print("Both conditions are True")
 9
10
11if __name__ == "__main__":
12    main()

Or

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 200
 5    b = 33
 6    c = 500
 7    if a > b or a > c:
 8        print("At least one of the conditions is True")
 9
10
11if __name__ == "__main__":
12    main()

Shorthand and Conditional Expressions

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 2
 5    b = 330
 6    if a > b: print("a is greater than b")
 7
 8
 9if __name__ == "__main__":
10    main()

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 2
 5    b = 330
 6    print("A") if a > b else print("B")
 7
 8
 9if __name__ == "__main__":
10    main()

Ternary Conditional Operator

Example:

 1#!/usr/bin/env python3
 2
 3def main():
 4    a = 2
 5    b = 330
 6    print("A") if a > b else print("B")
 7
 8
 9if __name__ == "__main__":
10    main()

Example:

1#!/usr/bin/env python3
2
3def main():
4    b = 330
5    print("A") if a > b else print("=") if a == b else print("B")
6
7
8if __name__ == "__main__":
9    main()