Conditionals
Conditionals are used to control the flow of a program. They allow us to execute certain blocks of code only if certain
conditions are met. In Python a conditional is created using the if
statement. The if
statement is followed by an
expression which is evaluated to a boolean value. If the expression evaluates to True
then the code block following
the if
statement is executed. If the expression evaluates to False
then the code block is skipped.
It is important to note that the code block following the if
statement is indented. This is how Python knows which
block of code is associated with the if
statement. The code block is indented by 4 spaces by convention and ends when
the indentation returns to the previous level.
if True:
print("This code block will be executed")
# > This code block will be executed
print("This code block will also be executed")
# > This code block will also be executed
print("This code block will be executed as well")
# > This code block will be executed as well
if False:
print("This code block will not be executed")
print("This code block will be executed as well")
# > This code block will be executed as well
if 1 == 1:
print("This code block will be executed")
# > This code block will be executed
if 1 == 2:
print("This code block will not be executed")
The if
statement can be followed by an else
statement. The else
statement is followed by a code block that will be
executed if the expression in the if
statement evaluates to False
.
if True:
print("This code block will be executed")
# > This code block will be executed
else:
print("This code block will not be executed")
if False:
print("This code block will not be executed")
else:
print("This code block will be executed")
# > This code block will be executed
The if
statement can also be followed by an elif
statement. The elif
statement is followed by an expression that
will be evaluated if the expression in the if
statement evaluates to False
. If the expression in the elif
statement evaluates to True
then the code block following the elif
statement will be executed. If the expression in
the elif
statement evaluates to False
then the code block following the elif
statement will be skipped.
if False:
print("This code block will not be executed")
elif True:
print("This code block will be executed")
# > This code block will be executed
else:
print("This code block will not be executed")
if False:
print("This code block will not be executed")
elif False:
print("This code block will not be executed")
else:
print("This code block will be executed")
# > This code block will be executed
The if
statement can be followed by any number of elif
statements, but an else
statement cannot
be followed by an elif
statement. The else
statement must be the last statement in the conditional.
if False:
print("This code block will not be executed")
elif False:
print("This code block will not be executed")
elif False:
print("This code block will not be executed")
else:
print("This code block will be executed")
# > This code block will be executed