6.1. Block If

6.1.1. Syntax

>>> 
... if <condition>:
...     <do something>

6.1.2. SetUp

Simulate user input (for test automation):

>>> from unittest.mock import MagicMock
>>> input = MagicMock(side_effect=['Mark Watney', ''])

6.1.3. Oneline Block

>>> if True:
...     print('First line of the true statement')
First line of the true statement

6.1.4. Multiline Blocks

>>> if True:
...     print('First line of the true statement')
...     print('Second line of the true statement')
...     print('Third line of the true statement')
First line of the true statement
Second line of the true statement
Third line of the true statement

6.1.5. Nested Blocks

>>> if True:
...     print('First line of the true statement')
...     print('Second line of the true statement')
...     if True:
...         print('First line of inner true statement')
First line of the true statement
Second line of the true statement
First line of inner true statement

6.1.6. Deeply Nested Blocks

>>> if True:
...     print('a')
...     print('b')
...     if True:
...         print('c')
...         print('d')
...         if True:
...             print('e')
...             if True:
...                 print('f')
...     if True:
...         print('g')
...         print('h')
...     print('i')
...     print('j')
a
b
c
d
e
f
g
h
i
j

6.1.7. Value Check

>>> age = 30
>>>
>>> if age >= 18:
...     print('adult')
adult

6.1.8. Boundary Check

>>> age = 7
>>>
>>> if 0 <= age < 18:
...     print('Age is between 0 and 18')
Age is between 0 and 18

Is equivalent to:

>>> age = 7
>>>
>>> if 0 <= age and age < 18:
...     print('Age is between 0 and 18')
Age is between 0 and 18

6.1.9. Nested Boundary Check

Checking if value is in range:

>>> a = 10
>>> b = 100
>>>
>>> if 0 <= a <= 50 < b:
...     print('Yes')
Yes

6.1.10. Checking If Empty

>>> name = input('What is your name?: ')  #input: Mark Watney
>>>
>>> if name:
...     print(f'My name is... {name}')
My name is... Mark Watney

Note, that following code is very error prone:

>>> name = input('What is your name?: ')  #input:
>>>
>>> if name is None:
...     print('Name is empty')

This will never print "Name is empty" because if user will not type any data just only hit the return key, variable name will hold an empty string not a None value!

>>> name
''

6.1.11. Conditional Assignment

  • Define variable based on evaluation

>>> country = 'USA'
>>>
>>> if country == 'USA':
...     job = 'astronaut'
>>>
>>> print(job)
astronaut

6.1.12. Use Case - 0x01

  • Even

>>> number = 4
>>>
>>> if number % 2 == 0:
...     print('even')
even