[New-bugs-announce] [issue20360] inspect.Signature could provide readable expressions for default values for builtins

[Larry Hastings]

New submission from Larry Hastings:

The signatures for builtins are stored as text and interpreted at runtime on demand.  inspect.Signature gets the default value for a parameter as a text string, which it evaluates (by hand, in a highly constrained way) to produce the parameter's value member.

Serhiy cleverly suggested that it'd be nice if Signature objects could also make this string available, as it's often more readable than the value.  For example, there's a parameter in zlib with the default "MAX_DECOMPRESSION - 1"; that turns into 7 I think.  Which would you prefer?

Right now there's no place to store this in the parameter object, so it can't happen for 3.4.  But perhaps in 3.5 we could add it, and figure out how to present it to the user.  For example __str__ could use it.


Thinking a little laterally: we *could* hide it in a *private* member on the Parameter object, then only use it for calculating __str__.  That would look so fancy!  Should we consider doing that for 3.4?

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messages: 208892
nosy: brett.cannon, larry, ncoghlan, serhiy.storchaka, yselivanov
priority: normal
severity: normal
stage: needs patch
status: open
title: inspect.Signature could provide readable expressions for default values for builtins
type: enhancement
versions: Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20360>
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