Importing Functions from Modules

Topics: import, function, module

Python’s power comes from its vast ecosystem of modules. Learning to import and use functions from modules effectively is crucial for productive programming.

Basic Import Statements

Below are the common ways to import functions that are already built by other people, i.e., the developers of the functions.

Import entire module

The import math code below actually imports the ‘module’ called math.

A module:

  • contains a single .py file containing Python codes
  • can define functions, classes, variables, or runnable codes
import math
result = math.sqrt(16)  # Use with module.function
print(result)           # 4.0

Import specific functions

From a package, we import only the functions we want.

Why we do not import all the functions inside a package?

  • a package contains a lot of modules and functions
  • importing all of it could slow down the importing process
  • however, you could import all of the functions IF you do not know which function you specifically want to use. Just use from package_name import *
from math import sqrt, pi, ceil

result = sqrt(25)  # Use directly without module name
area = pi * 5**2
rounded_up = ceil(4.2)

Import with alias

Importing a module as an alias has become a common practice for developers, programmers, and normal users of Python. Using an alias for a module means that instead of using the whole module name, you give it a short name… or nickname.

This just shortens the amount of time you type the module, but ultimately, makes the code cleaner and reduce the human error.

Example 1:

import math as m

result = m.factorial(5)
print(result)                    # 120

Example 2:

from math import factorial as fact

result = fact(5)
print(result)                    # 120

Example 3:

import numpy as np

array = np.array([1, 2, 3, 4])
mean_value = np.mean(array)
print(mean_value)                # 2.5

Common Built-in Modules

Math Module
import math

Basic mathematical operations

print(math.sqrt(16))        # Square root: 4.0
print(math.pow(2, 3))       # Power: 8.0, the same as 2^3
print(math.factorial(5))    # Factorial: 120, in mathematics, this is '5! = 5*4*3*2*1'

Trigonometric functions

print(math.sin(math.pi/2))  # Sine: 1.0
print(math.cos(0))          # Cosine: 1.0

Logarithms

print(math.log(10))         # Natural log
print(math.log10(100))      # Base-10 log: 2.0

Rounding and ceiling

print(math.ceil(4.2))       # Round up: 5 (this is the ceiling function)
print(math.floor(4.8))      # Round down: 4 (this is the floor function)

Constants

These are numbers in mathematics that do not end.

print(math.pi)              # 3.141592653589793
print(math.e)               # 2.718281828459045
Random Module
import random

Generate random numbers.

This can be used for randomization purposes. Remember when your panelists ask you how did you randomize your participants to be assigned in the Control Group, Treatment, etc.? This is it! Python can do that.

print(random.random())            # Float between   0-1
print(random.randint(1, 10))      # Integer between 1-10
print(random.uniform(1.5, 10.5))  # Float between   1.5-10.5

Work with sequences

fruits = ["apple", "banana", "orange", "grape"]
print(random.choice(fruits))    # Random choice
print(random.sample(fruits, 2)) # Random sample of 2 items

Shuffle a list

numbers = [1, 2, 3, 4, 5]
random.shuffle(numbers)
print(numbers)  # List is now shuffled

Set seed for reproducible results

random.seed(42)
print(random.randint(1, 100))  # Will always be the same with seed 42
Datetime Module

Import the datetime module

from datetime import datetime, date, timedelta

Current date and time

now = datetime.now()
today = date.today()

print(f"Current datetime: {now}")
print(f"Today's date: {today}")

Formatting dates

formatted_date = now.strftime("%Y-%m-%d %H:%M:%S")
print(f"Formatted: {formatted_date}")

Date arithmetic

tomorrow = today + timedelta(days=1)
next_week = today + timedelta(weeks=1)
past_date = today - timedelta(days=30)

print(f"Tomorrow: {tomorrow}")
print(f"Next week: {next_week}")
print(f"30 days ago: {past_date}")

Parse date strings

date_string = "2025-12-25"
christmas = datetime.strptime(date_string, "%Y-%m-%d")
print(f"Christmas: {christmas}")
OS Module

Import the os module

import os

Get current working directory

current_dir = os.getcwd()
print(f"Current directory: {current_dir}")

List files in directory

files = os.listdir(".")
print(f"Files in current directory: {files}")

Environment variables

user = os.getenv("USER", "Unknown")  # Get USER env var with default
print(f"Current user: {user}")

Path operations

file_path = os.path.join("data", "files", "example.txt")
print(f"File path: {file_path}")

Check if file/directory exists

print(f"Path exists: {os.path.exists(file_path)}")
Creating Import-Friendly Functions
# utils.py - A module you might create
def format_currency(amount, currency="USD"):
    """Format a number as currency."""
    return f"{currency} {amount:,.2f}"

Basic email validation

def validate_email(email):
    """Basic email validation."""
    return "@" in email and "." in email.split("@")[1]

Calculate tip amount

def calculate_tip(bill_amount, tip_percentage=15):
    """Calculate tip amount."""
    return bill_amount * (tip_percentage / 100)

# main.py - Using your module
from utils import format_currency, calculate_tip

Execute the function

bill = 85.50
tip = calculate_tip(bill, 18)
total = bill + tip

print(f"Bill: {format_currency(bill)}")
print(f"Tip: {format_currency(tip)}")
print(f"Total: {format_currency(total)}")
Writing Functions Modules