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 or equal to: a >= bThese conditions can be used in several ways, most commonly in "if statements" and loops.
An "if statement" is written by using the if keyword.
ExampleIf statement:
a = 33 b = 200 if b > a: print("b is greater than a") Try it Yourself »In this example we use two variables, a and b, which are used as part of the if statement to test whether b is greater than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we print to screen that "b is greater than a".
IndentationPython 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.
ExampleIf 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 Try it Yourself » ElifThe 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") Try it Yourself »In this example a is equal to b, so the first condition is not true, but the elif condition is true, so we print to screen that "a and b are equal".
ElseThe else keyword catches anything which isn't caught by the preceding conditions.
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") Try it Yourself »In this example a is greater than b, so the first condition is not true, also the elif condition is not true, so we go to the else condition and print to screen that "a is greater than b".
You can also he 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") Try it Yourself » Short Hand IfIf you he only one statement to execute, you can put it on the same line as the if statement.
ExampleOne line if statement:
if a > b: print("a is greater than b") Try it Yourself » Short Hand If ... ElseIf you he only one statement to execute, one for if, and one for else, you can put it all on the same line:
ExampleOne line if else statement:
a = 2b = 330print("A") if a > b else print("B") Try it Yourself »This technique is known as Ternary Operators, or Conditional Expressions.
You can also he multiple else statements on the same line:
ExampleOne line if else statement, with 3 conditions:
a = 330b = 330print("A") if a > b else print("=") if a == b else print("B") Try it Yourself » AndThe and keyword is a logical operator, and is used to combine conditional statements:
ExampleTest if a is greater than b, AND if c is greater than a:
a = 200b = 33c = 500if a > b and c > a: print("Both conditions are True") Try it Yourself » OrThe or keyword is a logical operator, and is used to combine conditional statements:
ExampleTest if a is greater than b, OR if a is greater than c:
a = 200b = 33c = 500if a > b or a > c: print("At least one of the conditions is True") Try it Yourself » NotThe not keyword is a logical operator, and is used to reverse the result of the conditional statement:
ExampleTest if a is NOT greater than b:
a = 33b = 200if not a > b: print("a is NOT greater than b") Try it Yourself » Nested IfYou can he if statements inside if statements, this is called nested if statements.
Example x = 41if x > 10: print("Above ten,") if x > 20: print("and also above 20!") else: print("but not above 20.")
Try it Yourself » The pass Statementif statements cannot be empty, but if you for some reason he an if statement with no content, put in the pass statement to oid getting an error.
Example a = 33b = 200if b > a: pass
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