Python 1-4

Python 1-4#

Modules, import, pip, testing

Modules and Packages#

  • A Module is a file containing Python code.

  • The Code in the module can be included in your code using the import command

  • A collection of modules bundled for re-distribution is known as a Package

Built in Modules vs. External#

  • The Python language has several modules which are included with the base language: Python Standard Library https://docs.python.org/3/library/

  • In addition you can import other libraries found on the Internet.

  • The Python Package Index is a website which allows you to search for other code avaialbe for use. https://pypi.org/

  • Once you know which package you want, you can install it with the pip command from the terminal.

  • example: pip install <name-of-package>

Requirements.txt#

  • requirements.txt is a file which stores the names of all the packages a project uses

  • adding them to the file is a replacement for installing each of them manually

  • to install the packages: pip install -r requirements.txt

Importing Modules#

Code in the module can be included in your code using the import command.

  • import foo imports all code from module foo

  • from foo import bar,baz only imports the bar and baz functions from module foo

  • import foo as f imports all code from module foo and renames it to f (usually to avoid naming conflicts)

Whats in the module?#

  • Use the dir(<module>) to list the functions in the module

  • Use help(module.function) to get the docstring for a function in a module.

1# Examples
2import math

1# get the functions
2dir(math)

['__doc__',
 '__file__',
 '__loader__',
 '__name__',
 '__package__',
 '__spec__',
 'acos',
 'acosh',
 'asin',
 'asinh',
 'atan',
 'atan2',
 'atanh',
 'cbrt',
 'ceil',
 'comb',
 'copysign',
 'cos',
 'cosh',
 'degrees',
 'dist',
 'e',
 'erf',
 'erfc',
 'exp',
 'exp2',
 'expm1',
 'fabs',
 'factorial',
 'floor',
 'fmod',
 'frexp',
 'fsum',
 'gamma',
 'gcd',
 'hypot',
 'inf',
 'isclose',
 'isfinite',
 'isinf',
 'isnan',
 'isqrt',
 'lcm',
 'ldexp',
 'lgamma',
 'log',
 'log10',
 'log1p',
 'log2',
 'modf',
 'nan',
 'nextafter',
 'perm',
 'pi',
 'pow',
 'prod',
 'radians',
 'remainder',
 'sin',
 'sinh',
 'sqrt',
 'tan',
 'tanh',
 'tau',
 'trunc',
 'ulp']

1help(math.pow)

Help on built-in function pow in module math:

pow(x, y, /)
    Return x**y (x to the power of y).

1math.pow(2,5) # 2*2*2*2*2

32.0

Challenge 1-4-1#

use the datetime module to:

parse a string like this “Month/Day/Year” 1/15/2025 into a datetime then print it like this: YYYY-MM-DD

For example in the current date is January 15, 2025 the output should be 2025-01-15

You will need to read through the module with dir() and help() or read the python docs to determine which functions to use.

Challenge 1-4-2#

Let’s make the code in 1-4-1 more resusable

re-write the date parse into a function parsedate_mdy(text: str) -> datetime:
re-write the date format into a function formatdate_ymd(date: datetime) -> str:
re-write the main program to use both functions. input -> parsedate -> formatdate -> output

Challenge 1-4-3#

Let’s make the code in 1-4-2 more resusable!!!

move your functions into a module names dateutils.py

import your functions from dateutils.py into 1-4-3.py

Testing Your Code#

  • For every function you write you should get in the habit of writing code to test the function

  • We want this to be automated so that we can easily determine if a change to our code has affected other code

  • This is especially useful with large projects

Assert#

assert is a python command which throws an exception if the expression asserted is false

When an assert fails, it raises an AssertionError exception which alerts us that something did not go as planned.

1assert 1 + 1 == 2   # This is true, no worries

1assert 2 + 2 == 5 # False AssertionError

---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
Cell In[11], line 1
----> 1 assert 2 + 2 == 5 # False AssertionError

AssertionError:

Pytest#

Pytest is testing framework for Python.

https://docs.pytest.org/en/stable/index.html

Pytest can automatically discover tests in your code. Any function that contains an assert will be executed when you invoke pytest.

You can invoke it at the terminal like this:

python -m pytest <filetotest>

The VS Code test plyugin should discover the tests

Challenge 1-4-4#

Automated testing for our module in 1-4-3

write two functions test_parsedate_mdy() and test_formatdate_ymd()in dateutils.py to test each of the two functions. Write two asserts for each function

Run pytest or VS Code test to make sure your tests pass!