Limiting scope of Python import

Question

I have some code that looks like this:

from pyparsing import Word, alphas, Optional, ...
# Do stuff ...
# And at the end, save a result to the outside world.
parser = ...

# Now use parser but don't use anything else from pyparsing again.

I like having the convenience of calling from <package> import <etc>, but I only want it to be used in a very small segment of code. I am afraid I am contributing to namespace pollution because I have a number of small snippets like this in the same file.

What is the Pythonic way of handling this situation? I am still just kind of playing around with it, so I would rather not write and rewritepyparsing. so many times.

Answer 1

The usual ways to control namespace pollution are

1. Delete the variables after use
2. Use the __all__ variable
3. Use import-as to underscored variable names

These techniques are all used by the core developers in the standard library. For example, the decimal module:

• starts out with private name imports such as import math as _math etc.

• Later it does work to setup a threading environment followed by variable deletion using del sys, MockThreading.

• In addition, it defines an __all__ variable to make clear what the public API is.

Taken together, these techniques keep the namespace as clean as a whistle.

Answer 2

One easy way is to use function scope to control import visibility within a file:

def prepare_parser():
    from pyparsing import Word, alphas, Optional, ...
    # do stuff, and get the final thing to return
    return ...

parser = prepare_parser()