Modules and imports — using other people's code

The three import styles

# 1 — the whole module
import math
math.sqrt(16)        # 4.0

# 2 — with an alias (the convention for big libraries)
import pandas as pd
pd.read_csv("file.csv")

# 3 — a specific name
from math import sqrt, pi
sqrt(16)             # 4.0
pi                   # 3.14159...

Standard library vs third party

• Standard library — comes with Python. No install needed. Examples: math, os, pathlib, datetime, json, csv, re.
• Third party — installed with pip install .... Examples: pandas, numpy, openpyxl, requests.

The conventional aliases

Use the conventions. Strangers reading your code will thank you.

Writing your own module

Any .py file is automatically importable from a script in the same folder. Put related functions in helpers.py:

# helpers.py
def clean_email(s):
    return s.strip().lower()

Then in main.py next to it:

from helpers import clean_email
clean_email("  ALICE@example.com ")   # 'alice@example.com'