python-by-example/06_modules_packages/01_imports.py

"""
================================================================================
File: 01_imports.py
Topic: Importing Modules and Packages in Python
================================================================================

This file demonstrates how to import and use modules in Python. Modules are
files containing Python code that can be reused across different programs.
Python's extensive standard library and third-party packages make imports
essential for productive development.

Key Concepts:
- import statement
- from ... import ...
- Aliasing with 'as'
- Built-in and standard library modules
- Relative imports

================================================================================
"""

# -----------------------------------------------------------------------------
# 1. Basic Import Statement
# -----------------------------------------------------------------------------
# Import entire module

print("--- Basic Import ---")

import math

# Access functions using module.function
print(f"math.pi = {math.pi}")
print(f"math.sqrt(16) = {math.sqrt(16)}")
print(f"math.ceil(3.2) = {math.ceil(3.2)}")
print(f"math.floor(3.8) = {math.floor(3.8)}")

# -----------------------------------------------------------------------------
# 2. Import Specific Items
# -----------------------------------------------------------------------------
# Import only what you need

print("\n--- From Import ---")

from math import pi, sqrt, pow

# Use directly without module prefix
print(f"pi = {pi}")
print(f"sqrt(25) = {sqrt(25)}")
print(f"pow(2, 8) = {pow(2, 8)}")

# Import multiple items
from datetime import date, time, datetime

today = date.today()
print(f"\nToday's date: {today}")

now = datetime.now()
print(f"Current datetime: {now}")

# -----------------------------------------------------------------------------
# 3. Import with Alias
# -----------------------------------------------------------------------------
# Rename modules or items for convenience

print("\n--- Import with Alias ---")

# Module alias
import random as rnd

print(f"Random number: {rnd.randint(1, 100)}")
print(f"Random choice: {rnd.choice(['apple', 'banana', 'cherry'])}")

# Common conventions
import collections as col
import json as json  # Usually kept as is
import os as os      # Usually kept as is

# Item alias
from math import factorial as fact
print(f"\nfact(5) = {fact(5)}")

# -----------------------------------------------------------------------------
# 4. Import All (Use Sparingly)
# -----------------------------------------------------------------------------
# Import everything from a module

print("\n--- Import All (Not Recommended) ---")

# from math import *  
# This imports everything, but:
# - Can cause naming conflicts
# - Makes it unclear where functions come from
# - Only use in interactive sessions if at all

# Better to be explicit about what you import

# -----------------------------------------------------------------------------
# 5. Useful Standard Library Modules
# -----------------------------------------------------------------------------

print("\n--- Standard Library Examples ---")

# os - Operating system interface
import os
print(f"Current directory: {os.getcwd()}")
print(f"Directory separator: {os.sep}")

# sys - System-specific parameters
import sys
print(f"\nPython version: {sys.version_info.major}.{sys.version_info.minor}")

# collections - Specialized containers
from collections import Counter, defaultdict

word_counts = Counter("mississippi")
print(f"\nCharacter counts: {dict(word_counts)}")

# Default dictionary
dd = defaultdict(list)
dd["fruits"].append("apple")
dd["fruits"].append("banana")
dd["vegetables"].append("carrot")
print(f"defaultdict: {dict(dd)}")

# json - JSON encoding/decoding
import json

data = {"name": "Alice", "age": 30}
json_string = json.dumps(data, indent=2)
print(f"\nJSON string:\n{json_string}")

# re - Regular expressions
import re

text = "Contact: john@email.com or jane@company.org"
emails = re.findall(r'\b[\w.-]+@[\w.-]+\.\w+\b', text)
print(f"Found emails: {emails}")

# itertools - Iteration utilities
from itertools import combinations, permutations

items = ['A', 'B', 'C']
print(f"\nCombinations of 2: {list(combinations(items, 2))}")
print(f"Permutations of 2: {list(permutations(items, 2))}")

# functools - Higher-order functions
from functools import lru_cache

@lru_cache(maxsize=100)
def fibonacci(n):
    """Cached fibonacci for performance."""
    if n < 2:
        return n
    return fibonacci(n-1) + fibonacci(n-2)

print(f"\nFibonacci(30): {fibonacci(30)}")
print(f"Cache info: {fibonacci.cache_info()}")

# -----------------------------------------------------------------------------
# 6. Checking Module Attributes
# -----------------------------------------------------------------------------

print("\n--- Module Attributes ---")

import math

# List all attributes/functions in a module
print("Math module functions (first 10):")
for name in dir(math)[:10]:
    print(f"  {name}")

# Module docstring
print(f"\nMath module doc: {math.__doc__[:50]}...")

# Module file location
print(f"Math module file: {math.__file__}")

# -----------------------------------------------------------------------------
# 7. Conditional Imports
# -----------------------------------------------------------------------------

print("\n--- Conditional Imports ---")

# Try to import, use fallback if not available
try:
    import numpy as np
    HAS_NUMPY = True
    print("NumPy is available")
except ImportError:
    HAS_NUMPY = False
    print("NumPy is NOT available")

# Another pattern
import sys
if sys.version_info >= (3, 9):
    from typing import Annotated  # Python 3.9+
else:
    print("Annotated not available (Python < 3.9)")

# -----------------------------------------------------------------------------
# 8. Module Search Path
# -----------------------------------------------------------------------------

print("\n--- Module Search Path ---")

import sys

print("Python searches for modules in:")
for i, path in enumerate(sys.path[:5]):  # First 5 paths
    print(f"  {i+1}. {path}")
print(f"  ... and {len(sys.path) - 5} more locations")

# Adding custom path (temporarily)
# sys.path.append('/my/custom/modules')

# -----------------------------------------------------------------------------
# 9. Import Patterns in Projects
# -----------------------------------------------------------------------------

print("\n--- Import Best Practices ---")

# Standard order for imports:
# 1. Standard library imports
# 2. Third-party imports
# 3. Local/project imports

# Example of well-organized imports:
"""
# Standard library
import os
import sys
from datetime import datetime
from typing import List, Dict

# Third-party (installed via pip)
import requests
import numpy as np
import pandas as pd

# Local/project modules
from myproject.utils import helper
from myproject.models import User
"""

print("Import order: Standard -> Third-party -> Local")
print("Group imports with blank lines between groups")

# -----------------------------------------------------------------------------
# 10. Practical Example: Building a Utility
# -----------------------------------------------------------------------------

print("\n--- Practical Example ---")

# Using multiple modules together
import os
import json
from datetime import datetime
from pathlib import Path

def get_system_info():
    """Gather system information using various modules."""
    return {
        "python_version": f"{sys.version_info.major}.{sys.version_info.minor}.{sys.version_info.micro}",
        "platform": sys.platform,
        "cwd": os.getcwd(),
        "home_dir": str(Path.home()),
        "timestamp": datetime.now().isoformat(),
        "path_separator": os.sep
    }

info = get_system_info()
print("System Info:")
print(json.dumps(info, indent=2))