Why do people write #!/usr/bin/env python on the first line of a Python script?

Question

It seems to me like the files run the same without that line.

Answer 1

It seems to me like the files run the same without that line.

If so, then perhaps you're running the Python program on Windows? Windows doesn't use that line—instead, it uses the file-name extension to run the program associated with the file extension.

However in 2011, a "Python launcher" was developed which (to some degree) mimics this Linux behaviour for Windows. This is limited just to choosing which Python interpreter is run — e.g. to select between Python 2 and Python 3 on a system where both are installed. The launcher is optionally installed as py.exe by Python installation, and can be associated with .py files so that the launcher will check that line and in turn launch the specified Python interpreter version.