Managing Python Versions on Windows

To handle multiple Python installations on Windows, use pyenv-win. Install it via command line:

pip install pyenv-win --target %USERPROFILE%\.pyenv

This tool simplifies version switching and environment management.

Foundational Python Concepts

Comments

Python supports single-line and multi-line comments.

Single-Line Comments

Begin with #; everything after is ignored.

# This is a comment
result = 5 + 3  # Calculation with inline comment

Multi-Line Comments

Use triple quotes (''' or """) for documentation strings, often serving as comments.

"""
This is a docstring.
It can span multiple lines.
Commonly used for function descriptions.
"""

def compute_total(value_a, value_b):
    """
    Adds two numbers.

    Parameters:
        value_a: First numeric input.
        value_b: Second numeric input.

    Returns:
        Sum of the inputs.
    """
    return value_a + value_b

Print Function

print() outputs various data types:

• Numbers
• Strings
• Expresssions with operators

Output destinations include displays and files. Control newlines with the end parameter.

print(42)  # Integer
print("text")  # String
print(7 * 6)  # Expression
print("line1", end=" ")  # No newline
print("line2")

Escape Sequences and Raw Strings

Escape sequences handle special characters:

• \\: Backslash
• \': Single quote
• \": Double quote
• \n: Newline
• \t: Tab

Use raw strings to disable escape processing by prefixing with r or R.

print("Path: C:\\Users\\file.txt")  # Escaped backslashes
print(r"Path: C:\Users\file.txt")  # Raw string
# Avoid trailing backslash in raw strings
print(r"example\path\\")  # Double backslash at end

Character Encoding

Convert between characters and binary representations.

print(ord('A'))  # Unicode code point
print(chr(0b1000001))  # Binary to character

Keywords and Identifiers

Keywords are reserved; view them with:

import keyword
print(keyword.kwlist)

Identifiers name variables, functions, etc. Rules:

• Use letters, digits, underscores
• Cannot start with a digit
• Case-sensitive
• Avoid keywords

Data Types

Basic Types

• Integer (int)
• Floating-point (float)
• Boolean (bool)
• String (str)

Container Types

• List (list): Mutable sequence
• Tuple (tuple): Immutable sequence
• Set (set): Unordered unique collection
• Dictionary (dict): Key-value mapping

Other Built-in Types

• NoneType: Represents null
• Bytes (bytes): Immutable binary data
• Bytearray (bytearray): Mutable binary data
• Range (range): Number sequence

Custom and Advanced Types

• Classes: User-defined types
• Frozenset: Immutable set
• Complex (complex): Complex numbers
• Generators and iterators

Sequences

Sequences include:

• String: Immutable Unicode
• List: Mutable
• Tuple: Immutable
• Range: Immutable numbers
• Bytes: Immutable binary
• Bytearray: Mutable binary

System and Package Management

Locate Python Installations

Find installed Python versions:

where python

Pip Commands

Manage Dependencies

Export and install from requirements file:

pip freeze > dependencies.txt
pip install -r dependencies.txt

Download Wheel Files

pip download package_name --only-binary :all:

Uninstall Packages

pip uninstall package_name

Configure Environment Variables

Set temporary Python path:

export PYTHONPATH=$PYTHONPATH:/path/to/package.whl

Verify installation:

python -c "import package; print(package.__version__)"

Package Source Configuration

Global Source

Edit pip.ini in C:\Users\[Username]\pip:

[global]
index-url = https://mirrors.aliyun.com/pypi/simple
[install]
trusted-host = mirrors.aliyun.com

Temporary Source

Specify source during installation:

pip install requests -i https://pypi.tuna.tsinghua.edu.cn/simple

Machine Learning Setup

NumPy and Jupyter

Install essential packages:

pip install jupyter numpy

Start Jupyter:

jupyter notebook

If pyzmq causes compatibility issues, rienstall a specific version:

pip uninstall pyzmq
pip install pyzmq==19.0.2

For Jupyter extensions in notebook 6.x, refer to documentation for plugin installation steps.

Bulk Package Removal

Uninstall all pip packages except core utilities:

pip freeze | grep -vE "^-e|^pip|^setuptools|^wheel" | xargs pip uninstall -y