Python Conditions and If 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.

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

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

Indentation

Python relies on indentation, using whitespace, to define scope in the code. Other programming languages often use curly-brackets for this purpose.

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

Elif

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

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:

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.

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:

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

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

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:

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:

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