Numbers are most common entities you will use when interacting with the computer. We represent numbers using numerical text in the editors, but store the numbers in variables.
Python is a dynamically typed language. We do not have declare a type of a variable before assigning any value to it.
Let's start with a simple exercise of finding if a year is a leap year
- A normal year has 365 days
- A leap year has 366 days.
A Leap year is a year
- That is exactly divisible by 4. (2016, 2020, 2024) ** If divisible 100, then it is not. (2100, 2200, 2300) *** If it is divisible by 400, then it is. (2000, 2400)
Refer to Maths is Fun for more information on leap years.
def test_is_leap_year():
assert is_leap_year(2016) == True
assert is_leap_year(2020) == True
assert is_leap_year(2024) == True
assert is_leap_year(2100) == False
assert is_leap_year(2200) == False
assert is_leap_year(2300) == False
assert is_leap_year(2000) == True
assert is_leap_year(2400) == True
If we run pytest on this.
def test_is_leap_year():
> assert is_leap_year(2016) == True
E NameError: name 'is_leap_year' is not defined
numbers/leap_year_1.py:3: NameError
=======================================
The NameError means that we have not defined our method yet. The error message clearly says that is_leap_year
is
not defined. So, let us define it.
def is_leap_year(param):
pass
def test_is_leap_year():
assert is_leap_year(2016) == True
assert is_leap_year(2020) == True
assert is_leap_year(2024) == True
assert is_leap_year(2100) == False
assert is_leap_year(2200) == False
assert is_leap_year(2300) == False
assert is_leap_year(2000) == True
assert is_leap_year(2400) == True
Let us exercise the tests again.
$ pytest numbers/leap_year_2.py
def test_is_leap_year():
> assert is_leap_year(2016) == True
E assert None == True
E + where None = is_leap_year(2016)
numbers/leap_year_2.py:6: AssertionError
This time the error message means that our output is not equal to the expected value.
def is_leap_year(year: int) -> bool:
"""
:param year Given year to test, whether it is a leap year
:return: True if leap year, False otherwise
"""
if year % 4 == 0:
if year % 100 == 0:
if year % 400 == 0:
return True
return False
return True
return False
def test_is_leap_year():
assert is_leap_year(2016) == True
assert is_leap_year(2020) == True
assert is_leap_year(2024) == True
assert is_leap_year(2100) == False
assert is_leap_year(2200) == False
assert is_leap_year(2300) == False
assert is_leap_year(2000) == True
assert is_leap_year(2400) == True
$ pytest numbers/leap_year_3.py
numbers/leap_year_3.py .
Our tests are successful.
There are ways in which we could short-circuit the conditions. In this book, I want to emphasize that refactor for code-repeatability, but keep the code as you understand it best. If you the conditions reflect what you are looking for the code is complete.
Here is the final code for the test leap year.
def is_leap_year(year: int) -> bool:
"""
:param year Given year to test, whether it is a leap year
:return: True if leap year, False otherwise
"""
# divisible by 4, True
if year % 4 == 0:
# divisible by 10, False
if year % 100 == 0:
# divisible by 400, True
if year % 400 == 0:
return True
return False
return True
return False
def test_is_leap_year():
assert is_leap_year(2016) == True
assert is_leap_year(2020) == True
assert is_leap_year(2024) == True
assert is_leap_year(2100) == False
assert is_leap_year(2200) == False
assert is_leap_year(2300) == False
assert is_leap_year(2000) == True
assert is_leap_year(2400) == True
assert is_leap_year(2019) == False