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# Package Installation
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Comprehensive package installation capabilities including dependency resolution, version control integration, and support for multiple package sources and formats.
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## Capabilities
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### Basic Installation
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Install packages from PyPI with automatic dependency resolution.
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```bash { .api }
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# Install latest version
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pip install package_name
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# Install specific version
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pip install package_name==1.2.3
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# Install version with constraints
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pip install "package_name>=1.0,<2.0"
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pip install "package_name~=1.2.0"  # Compatible release
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# Install multiple packages
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pip install package1 package2 package3
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```
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### Requirements File Installation
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Install packages from requirements files with dependency locking and constraint handling.
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```bash { .api }
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# Install from requirements file
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pip install -r requirements.txt
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# Install from multiple requirements files
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pip install -r requirements.txt -r dev-requirements.txt
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# Install with constraints
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pip install -r requirements.txt -c constraints.txt
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```
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Requirements file format:
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```text
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# Direct dependencies
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requests==2.28.1
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django>=4.0,<5.0
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# VCS dependencies
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git+https://github.com/user/repo.git@v1.0#egg=package_name
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# Local dependencies
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-e ./local_package
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/path/to/local/package.tar.gz
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# Index options
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--index-url https://pypi.org/simple/
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--extra-index-url https://test.pypi.org/simple/
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# Installation options
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--no-deps
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--force-reinstall
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```
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### Version Control Installation
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Install packages directly from version control repositories with branch, tag, and commit support.
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```bash { .api }
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# Git repositories
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pip install git+https://github.com/user/repo.git
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pip install git+https://github.com/user/repo.git@branch_name
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pip install git+https://github.com/user/repo.git@tag_name
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pip install git+https://github.com/user/repo.git@commit_hash
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# With subdirectory
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pip install "git+https://github.com/user/repo.git#subdirectory=pkg_dir"
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# With specific name
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pip install "git+https://github.com/user/repo.git#egg=package_name"
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# SSH URLs
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pip install git+ssh://git@github.com/user/repo.git
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# Other VCS systems
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pip install svn+https://svn.example.com/repo/trunk/
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pip install hg+https://bitbucket.org/user/repo
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pip install bzr+https://launchpad.net/user/repo
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```
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### Local Installation
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Install packages from local files, directories, and development installations.
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```bash { .api }
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# Install from local directory
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pip install /path/to/package/
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# Install from archive
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pip install /path/to/package.tar.gz
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pip install /path/to/package.whl
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# Editable/development installation
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pip install -e /path/to/package/
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pip install -e .  # Current directory
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# Install from URL
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pip install https://example.com/package.tar.gz
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```
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### Advanced Installation Options
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Control installation behavior with various options and flags.
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```bash { .api }
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# Installation modes
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pip install --user package_name           # User installation
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pip install --system package_name         # System installation
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pip install --target /path/to/dir package_name  # Target directory
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# Dependency handling
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pip install --no-deps package_name        # Skip dependencies
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pip install --force-reinstall package_name  # Force reinstall
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pip install --upgrade package_name        # Upgrade to latest
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pip install --upgrade-strategy eager package_name  # Upgrade dependencies
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# Build options
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pip install --no-binary :all: package_name     # Build from source
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pip install --only-binary :all: package_name   # Only use wheels
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pip install --prefer-binary package_name       # Prefer wheels
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pip install --no-build-isolation package_name  # Disable build isolation
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# Index options
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pip install --index-url https://pypi.org/simple/ package_name
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pip install --extra-index-url https://test.pypi.org/simple/ package_name
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pip install --trusted-host pypi.org package_name
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pip install --find-links /path/to/dir package_name
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# Caching
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pip install --no-cache-dir package_name   # Disable cache
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pip install --cache-dir /path/to/cache package_name  # Custom cache
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# Verbosity and output
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pip install --verbose package_name        # Verbose output
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pip install --quiet package_name          # Minimal output
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pip install --progress-bar off package_name  # Disable progress bar
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```
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### Hash Verification
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Install packages with cryptographic hash verification for security.
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```bash { .api }
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# Using requirements file with hashes
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pip install --require-hashes -r requirements.txt
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```
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Requirements file with hashes:
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```text
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requests==2.28.1 \
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    --hash=sha256:7c5599b102feddaa661c826c56ab4fee28bfd17f5abca1ebbe3e7f19d7c97ddf \
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    --hash=sha256:8fefa2a1a1365bf5520aac41836fbee479da67864514bdb821f31ce07ce65349
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```
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### Environment Variables
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Control pip behavior through environment variables.
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```bash { .api }
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# Index configuration
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export PIP_INDEX_URL=https://pypi.org/simple/
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export PIP_EXTRA_INDEX_URL=https://test.pypi.org/simple/
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export PIP_TRUSTED_HOST=pypi.org
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# Installation options
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export PIP_USER=1                    # User installation
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export PIP_NO_CACHE_DIR=1           # Disable cache
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export PIP_REQUIRE_VIRTUALENV=1     # Require virtual environment
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# Timeouts and retries
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export PIP_TIMEOUT=60
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export PIP_RETRIES=3
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# Proxy configuration
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export PIP_PROXY=http://user:password@proxy.server:port
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```
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### Installation in Virtual Environments
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Pip respects virtual environment activation and provides isolation.
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```bash { .api }
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# Using venv
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python -m venv myenv
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source myenv/bin/activate  # On Windows: myenv\Scripts\activate
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pip install package_name
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# Using conda
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conda create -n myenv python=3.9
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conda activate myenv
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pip install package_name
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# Require virtual environment
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pip install --require-virtualenv package_name
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export PIP_REQUIRE_VIRTUALENV=1
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```
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### Programmatic Installation
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Use subprocess for programmatic package installation (recommended approach).
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```python { .api }
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import subprocess
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import sys
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def install_package(package_name, upgrade=False, user=False):
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    """Install a Python package using pip."""
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    cmd = [sys.executable, '-m', 'pip', 'install']
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    if upgrade:
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        cmd.append('--upgrade')
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    if user:
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        cmd.append('--user')
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    cmd.append(package_name)
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    try:
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        subprocess.check_call(cmd)
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        print(f"Successfully installed {package_name}")
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    except subprocess.CalledProcessError as e:
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        print(f"Failed to install {package_name}: {e}")
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        raise
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def install_requirements(requirements_file):
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    """Install packages from requirements file."""
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    cmd = [sys.executable, '-m', 'pip', 'install', '-r', requirements_file]
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    try:
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        subprocess.check_call(cmd)
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        print(f"Successfully installed from {requirements_file}")
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    except subprocess.CalledProcessError as e:
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        print(f"Failed to install from {requirements_file}: {e}")
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        raise
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# Usage examples
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install_package('requests')
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install_package('django', upgrade=True)
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install_requirements('requirements.txt')
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```