let3 documentation


Assign variables wherever, whenever you want.


let3 is a strict fork of Taylor Marks’s let package with a fix allowing to work with Python3 or higher and with a little code reformatting and minor improvements.

PyPI record.


Overview below is a copy from the original let website (with only the necessary changes regarding let3).

Quick Start

Once you’ve installed, you can really quickly verified that it works with just this:

>>> from let import let
>>> if let(count = len("Hello World!")):
...     print(count)


In C, Java, and many other languages, it’s possible to assign variables inside of if or while condition statements. This is useful in allowing you to concisely both assign the value, and check whether a condition is met.

This ability doesn’t exist in Python, because of the thought that when people write something like:

if row = db.fetch_results():

They may have actually meant:

if row == db.fetch_results():

Personally, I have never made this mistake. It seems far more like a theoretical mistake that could plausibly happen than one that actually happens and warrants removing features, as was chosen in Python.

Anyways, the let function in this module gives you something very close to that ability in other languages. A few examples:

if let(name = longInstanceName.longAttributeName):

# Yes, db.fetch_results() should just return a generator. No, it doesn't.
while let(results = db.fetch_results()):

if let(count = len(nameValuePair)) != 1:
    raise Exception(f"Bad amount: {count}")



To install run:

python -m pip install --upgrade let3



  • Development is strictly based on tox. To install it run:

    python -m pip install --upgrade tox

Visit development page.

Installation from sources:

clone the sources:

and run:

python -m pip install ./let3

or on development mode:

python -m pip install --editable ./let3


Copyright (c) 2016 Taylor Marks
Copyright (c) 2016-2022 Adam Karpierz
Licensed under the MIT License
Please refer to the accompanying LICENSE file.


Indices and tables