what is python library

Python library refers to a collection of codes in python that completes certain functions and is a combination of codes for users to use; in python, libraries are in the form of packages and modules; where python modules are contained and organized code snippets. A python package is a hierarchical file directory structure.

Friends who are new to python must encounter such a problem, python modules, python packages, python libraries... I feel confused, let me talk about it today What are the differences between modules, libraries, and packages in Python?

1. python module is:

python module: Contains and organized code snippets as modules.

The expression is: the written code is saved as a file. This file is a module. sample.py where the file name smaple is the module name.

Relationship diagram:

2. The python package is:

The package is A hierarchical file directory structure that defines a python application execution environment consisting of n modules or n sub-packages. In layman's terms: a package is a directory containing an __init__.py file. This directory must have this __init__.py file and other modules or sub-packages.

FAQ:

Introduce a module under a specific path

Use sys.path.append(yourmodulepath)

Add a path to the python system path to avoid specifying the path through code every time

Use the system environment variable export PYTHONPATH=$PYTHONPATH:yourmodulepath,

directly add this The path links to a directory similar to /Library/Python/2.7/site-packages

Good advice:

Always use if __name__ == '__main__', make sure to write The package can be imported or run independently for testing.

Multiple imports will not execute the module multiple times, but only once. You can use reload to force the module to run, but it is not recommended.

The common package structure is as follows:

package_a├── __init__.py├── module_a1.py└── module_a2.pypackage_b├── __init__.py├ ── module_b1.py└── module_b2.py

main.py

If main.py wants to reference the module modulea1 in packagea, you can use:

from package_a import module_a1

import package_a.module_a1

If modulea1 in packagea needs to reference packageb, then by default, python cannot find packageb . We can use sys.path.append('../'), add this sentence to __init__.py in packagea, and then add * import __init_ to all modules in the package.

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##3. Library (library)

The concept of a library is to have A collection of related functional modules. This is also one of the major features of Python, that is, it has a powerful standard library, third-party libraries and custom modules.

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