Is it necessary to specify the version of each library used in the requirements.txt file?

Yes, it is necessary to specify the versions of used libraries in the requirements.txt file.

Main reasons:

• Reproducibility of the environment: Ensures that the same library versions are used when installing dependencies on another machine or environment as during development. This prevents issues related to version incompatibility.
• Fixing the working state: Allows "freezing" the set of libraries with which the project works successfully. This is useful for deployment as well as for rolling back to a previous stable state.
• Dependency control: Clearly indicates which versions are used, simplifying debugging and updating libraries in the future.

Ways to specify versions:

Method	Description	Example
Exact match	Specifies a specific version. The strictest method.	requests==2.28.1
Minimum version	Requires a version not lower than the specified one.	requests>=2.28.1
Not lower, but lower than	Requires a version not lower than the first specified, but lower than the second (excluding it).	requests>=2.28.1,<3.0

Using pip freeze > requirements.txt is a common way to generate a requirements.txt with exact versions based on the current virtual environment.