Popular recipes tagged "variables"

Variable Abbreviations (Python)

2017-06-22T11:57:20-07:00

Python recipe 580807 by Alfe (abbreviations, contextmanager, variables, with).

One sometimes has nice long speaking names vor variables, maybe things like buildingList[foundIndex].height, but would like to address these in a shorter fashion to be used within a formula or similar where lots of longs names tend to confuse any reader trying to understand the formula. Physicists use one-letter names for a reason.

For this I wrote a small context provider which allows using short names instead of long ones:

with Abbr(h=buildingList[foundIndex].height, g=gravitationalConstant):
    fallTime = sqrt(2 * h / g)
    endSpeed = sqrt(2 * h * g)
print("Fall time:", fallTime)
print("End speed:", endSpeed)

For longer formulas this can reduce ugly multi-line expressions to clearly readable one-liners.

One could use this:

h = buildingList[foundIndex].height
g = gravitationalConstant
fallTime = sqrt(2 * h / g)
endSpeed = sqrt(2 * h * g)
del g, h
print("Fall time:", fallTime)
print("End speed:", endSpeed)

to achieve the same result, but

it would not look as clean and
the context provider solves the typical issues like cleanup on exception etc.

Just using local variables without cleanup (like above without the del statement) also is an option of course, but that would clutter the variable name space unnecessarily.

CAVEATS: The implementation of Abbr() is a hack. If used as intended and described here, it should work just fine, though. But the hackish nature forces me to mention some things: Since at compile time the compiler decides that the h and g in the example must be global variables (because they aren't assigned in the function), it produces byte code accessing global variables. The context provider changes the global variable structure to fill the needs. (Overridden already existing global variables of the same name get restored properly at context exit.) This means some things:

One cannot have a local variable of the same name in the frame surrounding the context manager.
Existing global variables are changed during the time of the context manager; so using names like sys or os for abbreviations might be a bad idea due to side-effects.

Decorator to expose local variables of a function after execution (Python)

2010-07-07T22:01:23-07:00

Python recipe 577283 by Pietro Berkes (decorator, function, inner, local, scope, variables). Revision 2.

Decorator to expose the local variables defined in the inner scope of a function. At the exit of the decorated function (regular exit or exceptions), the local dictionary is copied to a read-only property, locals.

The main implementation is based on injecting bytecode into the original function, and requires the lightweight module byteplay (available here). See below for an alternative implementation that only uses the standard library.

Decorator to expose local variables of a function after execution [alternative implementation] (Python)

2010-07-08T09:44:28-07:00

Python recipe 577295 by Andrea Maffezzoli (decorator, function, inner, local, scope, variables). Revision 6.

Please note that the present is a fork of the recipe 577283 "Decorator to expose local variables of a function after execution" of Pietro Berkes, available at http://code.activestate.com/recipes/577283-decorator-to-expose-local-variables-of-a-function-/ , and aiming only to report the alternative implementation "persistent_locals2", whose I'm co-author with Pietro Berkes, and which was submitted together to the original recipe. Refer to the latter for an exhaustive description and discussion.

Class to calculate increment of variables based on time (units per seconds) (Python)

2008-08-18T16:29:08-07:00

Python recipe 576424 by nosklo (increment, linear, number, time, units_per_second, variables). Revision 3.

A simple calculation of small increments to be applied to a variable, given the variable time that has passed since last update, to make a linear increase over time (in units per second).