Python If Else and Code Branching

April 23, 2019  

Python, like most programming languages, has an if statement that provides branching in your code. An example syntax of Python’s if statement:

x = 3
y = 4

if x == y:
    print("They are equal")
else:
    print("They are not equal")

The else branch is optional:

if x == y:
    print("They are equal")

The expression can be anything that evaluates a True or False
Example:

  1. if num >= 5:
  2. if str == “What’s up?”:
  3. if this != that:
  4. if SomeVar:

Take note of example 4 above — in Python, anything that does not equate to zero, Null, or an empty object is True.
Example:

>>> s = 0
>>> if s:
...     print("True")
...    # Python returns nothing - statement is false
>>> s = 1
>>> if s:
...     print("True")
...
>>> s = " "
>>> if s:
...     print("True")
...     # Nothing again- statement is false
>>> s = "Hello"
>>> if s:
...     print("True")
...     
True

Python includes comprehensive range of boolean operators you can use within your expressions:

- < is Less than
- <= is Less than equal
- > is Greater than
- >= is Greater than or equal
- == is Equal
- != is Not equal
- is Is a particular object
- is not Is not a particular object

Boolean operations are also supported for negating and chaining expressions:

or is Either expression can be True
and is Both expressions must be True
not is Negate the preceeding expression
Python also supports multiple branching using the elif statement:

if [exp1 is True]:
   # execute if exp1 is True
elif [exp2 is True]:
   # execute if exp2 is True
elif [exp3 is True]:
   # execute if exp2 is True

REFERENCE:

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