Module self-reference makes it impossible to access code in prettyprinter.py

[macdjord]

• PrettyPrinter version: 0.18.0
• Python version: 3.11.2
• Operating System: Win10

Description

I tried to import prettyprinter/prettyprinter.py so that I could properly type-hint the 'context' argument to my custom printer function. However, when I did so, I was informed that prettyprinter.prettyprinter did not contain any attribute PrettyContext.

On investigation, I discovered that prettyprinter (the package corresponding to prettyprinter/) contains, on initial import, already contains a member named prettyprinter, but this member is actually just a circular reference to the package itself. This makes it impossible to import prettyprinter.prettyprinter (the module corresponding to prettyprinter/prettyprinter.py).

What I Did

import prettyprinter as _prettyprinter
import prettyprinter.doctypes as __
import prettyprinter.prettyprinter as __


class Timestamp:
    ...


@_prettyprinter.register_pretty(Timestamp)
def pretty_timestamp(
        timestamp: Timestamp,
        ctx: _prettyprinter.prettyprinter.PrettyContext,
) -> _prettyprinter.doctypes.Doc:
    ...

Output:

Traceback (most recent call last):
  File "[REDACTED]/test.py", line 13, in <module>
    ctx: _prettyprinter.prettyprinter.PrettyContext,
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: module 'prettyprinter' has no attribute 'PrettyContext'

import prettyprinter as _prettyprinter
print(f"{_prettyprinter=}")
print(f"{_prettyprinter.prettyprinter=}")
import prettyprinter.prettyprinter as _pp_pp
print(f"{_pp_pp=}")
print(f"{_pp_pp.prettyprinter=}")

Output:

_prettyprinter=<module 'prettyprinter' from 'C:\\Python311\\Lib\\site-packages\\prettyprinter\\__init__.py'>
_prettyprinter.prettyprinter=<module 'prettyprinter' from 'C:\\Python311\\Lib\\site-packages\\prettyprinter\\__init__.py'>
_pp_pp=<module 'prettyprinter' from 'C:\\Python311\\Lib\\site-packages\\prettyprinter\\__init__.py'>
_pp_pp.prettyprinter=<module 'prettyprinter' from 'C:\\Python311\\Lib\\site-packages\\prettyprinter\\__init__.py'>

The Fix

This is caused by the following line in prettyprinter/__init__.py:

import prettyprinter.pretty_stdlib

As well as actually importing the pretty_stdlib module, this also, as a side-effect, adds a member to package prettyprinter whose value is the package prettyprinter. (Actually, I'm amazed this doesn't cause an import cycle error.)

The fix is to change that line to:

from . import pretty_stdlib

Or:

import prettyprinter.pretty_stdlib as __

Workaround

Until this bug is fixed, this is a workaround:

import prettyprinter as _prettyprinter
del _prettyprinter.prettyprinter
import prettyprinter.prettyprinter as _pp_pp

Note that with this workaround you can only access the prettyprinter.py code using _pp_pp; trying to do _prettyprinter.prettyprinter will not work.