Python markers and compatibility tags with requirements.txt

I am not an expert in python, but I am trying to understand a bit more about it and if my current knowledge is correct.

For requirement.txt we have markers that can be added to the file, if I understand correctly those markers are used to express what environment I want it to work on, for example, sys_platform=“windows” I need the dependency for windows and the same for python version and others.

From PEP 345 – Metadata for Python Software Packages 1.2 | we have those markers

python_version = ‘%s.%s’ % (sys.version_info[0], sys.version_info[1])
python_full_version = sys.version.split()[0] =
sys.platform = sys.platform
platform.version = platform.version()
platform.machine = platform.machine()
platform.python_implementation = platform.python_implementation()

Now, we also have compatibility tags from PEP 425 – Compatibility Tags for Built Distributions |, the names are similar to the markers, so I am a bit confused, are they the same? some tags we have are

So I have some questions:

  1. Are markers equivalents of the compatibility tags, for example, sys_platform is the platform tag or the ABI tag to the python_version marker? is there any equivalent between those values?
  2. If I want to know what’s the real dependency I am using how I can know, I mean if I am using “pandas” how I can know using either compatibility tags or markers that I am using, for example, the one for mac for python 2.7 in the requirements.txt?
  3. Can I set those markers/tags when installing a dependency?
  4. I want to have more specific information about the component I am using, maybe compatibility tags in the requirements.txt, is that possible?