Python If Else and Code Branching

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:

Build your first website with Python and Django: Build and Deploy a website with Python & Django

 

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