conditional.py

"""
This module shows how to use if blocks, if-else blocks and if-elif-else
blocks to decide which lines of code to run (and skip).
"""


def main() -> None:
 x = 1
 x_add_two = x + 2

 # This condition is obviously true
 ran_1 = False
 if x_add_two == 3: # skip: else
 ran_1 = True # run
 assert ran_1 is True

 # A negated condition can also be true
 ran_2 = False
 if not x_add_two == 1: # skip: else
 ran_2 = True # run
 assert ran_2 is True

 # There are `else` statements as well, which run if the initial condition
 # fails. Notice that one line gets skipped and this conditional does not
 # help us make a conclusion on the variable's true value
 if x_add_two == 1:
 ran_3 = False # skip: if
 else:
 ran_3 = True # run
 assert ran_3 is True

 # The `else` statement also runs once all other `if` and `elif` conditions
 # fail. Notice that multiple lines get skipped, and that all the
 # conditions could have been compressed to `x_add_two != 3` for
 # simplicity. In this case, less logic results in more clarity
 if x_add_two == 1:
 ran_4 = False # skip: if
 elif x_add_two == 2:
 ran_4 = False # skip: if
 elif x_add_two < 3 or x_add_two > 3:
 ran_4 = False # skip: if
 else:
 ran_4 = True # run
 assert ran_4 is True

 # Conditionals can also be written in one line using `if` and `else`
 # with the following form: A if condition else B. This can be used
 # for assignments as shown below
 ran_5 = False
 ran_5 = True if x_add_two == 3 else False
 assert ran_5 is True

 # Python is one of the few programming languages that allows chained
 # comparisons. This is useful for checking if a variable is within
 # a range of values. You can see that in this example, the expression
 # `0 < x_add_two < 2` is equivalent to `x_add_two > 0 and x_add_two < 2`
 ran_6 = False
 if 0 < x_add_two < 2:
 ran_6 = False # skip: if
 else:
 ran_6 = True # run
 assert ran_6 is True


if __name__ == "__main__":
 main()