📥 Imports

The import system is how Python finds and loads code from other files. Understanding imports is essential for organizing larger projects.

---

✅ Basic Import Syntax

# Import the whole module
import math
print(math.sqrt(16))  # 4.0

# Import specific names
from math import sqrt, pi
print(sqrt(16))  # 4.0

# Import with alias
import numpy as np
from datetime import datetime as dt

---

✅ What Happens During Import

When you import a module, Python:

1. Searches for the module in sys.path
2. Compiles the .py file to bytecode (cached in __pycache__)
3. Executes the module code once
4. Caches the module in sys.modules

Subsequent imports of the same module use the cached version.

---

✅ The Search Path (sys.path)

Python looks for modules in this order:

import sys
print(sys.path)
# ['', '/usr/lib/python3.x', '/usr/lib/python3.x/site-packages', ...]

1. Current directory (or script directory)
2. PYTHONPATH environment variable directories
3. Standard library directories
4. Site-packages (installed packages)

---

✅ Import Styles

# Style 1: Import module (preferred for large modules)
import os
os.path.join("a", "b")  # Clear where join comes from

# Style 2: Import specific names (good for frequently used items)
from os.path import join, exists
join("a", "b")  # Shorter, but origin less clear

# Style 3: Import all (generally avoid)
from os.path import *  # Pollutes namespace, hard to track origins

---

✅ Common Import Patterns

# Standard library first, then third-party, then local
import os
import sys

import requests
import numpy as np

from myproject import utils
from myproject.models import User

---

🔍 Key Takeaways

• import module vs from module import name have different use cases.
• Python caches imports in sys.modules for efficiency.
• The search path (sys.path) determines where Python looks for modules.
• Follow PEP 8 import ordering: stdlib, third-party, local.

---

Back: Module 13 README | Next: Creating Modules