When to use os.name, sys.platform, or platform.system?

Dived a bit into the source code.

The output of sys.platform and os.name are determined at compile time. platform.system() determines the system type at run time.

• sys.platform is specified as a compiler define during the build configuration.
• os.name checks whether certain os specific modules are available (e.g. posix, nt, …)
• platform.system() actually runs uname and potentially several other functions to determine the system type at run time.

My suggestion:

• Use os.name to check whether it’s a posix-compliant system.
• Use sys.platform to check whether it’s a linux, cygwin, darwin, atheos, etc.
• Use platform.system() if you don’t believe the other sources.