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Python Conditional Statements

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

These conditions can be used in several ways, most commonly in "if statements" and loops.

If Statement​

An "if statement" is written by using the if keyword.

Example​

a = 33
b = 200
if b > a:
  print("b is greater than a")

Indentation​

Python relies on indentation (whitespace at the beginning of a line) to define scope in the code. Other programming languages often use curly-brackets for this purpose.

Example​

If statement, without indentation (will raise an error):

a = 33
b = 200
if b > a:
print("b is greater than a")  # you will get an error

Elif​

The elif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".

Example​

a = 33
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")

Else​

The else keyword catches anything which isn't caught by the preceding conditions. if else image

Example​

a = 200
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")
else:
  print("a is greater than b")

You can also have an else without the elif:

Example​

a = 200
b = 33
if b > a:
  print("b is greater than a")
else:
  print("b is not greater than a")

Short Hand If​

If you have only one statement to execute, you can put it on the same line as the if statement.

Example​

One line if statement:

if a > b: print("a is greater than b")

Short Hand If ... Else​

If you have only one statement to execute, one for if, and one for else, you can put it all on the same line.

Example​

One line if else statement:

a = 2
b = 330
print("A") if a > b else print("B")

This technique is known as Ternary Operators, or Conditional Expressions.

You can also have multiple else statements on the same line:

Example​

One line if else statement, with 3 conditions:

a = 330
b = 330
print("A") if a > b else print("=") if a == b else print("B")

And​

The and keyword is a logical operator, and is used to combine conditional statements.

Example​

Test if a is greater than b, AND if c is greater than a:

a = 200
b = 33
c = 500
if a > b and c > a:
  print("Both conditions are True")

Or​

The or keyword is a logical operator, and is used to combine conditional statements.

Example​

Test if a is greater than b, OR if a is greater than c:

a = 200
b = 33
c = 500
if a > b or a > c:
  print("At least one of the conditions is True")

Not​

The not keyword is a logical operator, and is used to reverse the result of the conditional statement.

Example​

Test if a is NOT greater than b:

a = 33
b = 200
if not a > b:
  print("a is NOT greater than b")

Nested If​

You can have if statements inside if statements; this is called nested if statements.

Example​

x = 41

if x > 10:
  print("Above ten,")
  if x > 20:
    print("and also above 20!")
  else:
    print("but not above 20.")

The pass Statement​

If statements cannot be empty, but if you, for some reason, have an if statement with no content, put in the pass statement to avoid getting an error.

Example​

a = 33
b = 200

if b > a:
  pass

This documentation covers the basics of Python conditional statements, including if, elif, else, nested if statements, and logical operators. Proper indentation and examples are provided for clarity.