[issue19290] Clarify compile and eval interaction.

[Terry J. Reedy]

Change by Terry J. Reedy :


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versions: +Python 3.11 -Python 2.7, Python 3.3, Python 3.4

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[issue19290] Clarify compile and eval interaction.

[Ezio Melotti]

Ezio Melotti added the comment:

I find your suggestion difficult to read.  Maybe using a list would make it 
more understandable?

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nosy: +ezio.melotti
type:  - enhancement

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[issue19290] Clarify compile and eval interaction.

[Terry J. Reedy]

New submission from Terry J. Reedy:

This issue was stimulated by #17294 where there seems to be some confusion over 
the purpose of the compile modes with regards to return values. I then noticed 
that the eval doc starts wrong and later corrects itself.

I think the following sentence from the compile doc could be improved. The 
current version:

The mode argument specifies what kind of code must be compiled; it can be 
'exec' if source consists of a sequence of statements, 'eval' if it consists of 
a single expression, or 'single' if it consists of a single interactive 
statement (in the latter case, expression statements that evaluate to something 
other than None will be printed).

My suggestion:

The mode argument specifies the allowed source and the return value when the 
result is passed to eval(). It can be 'exec' for any source (a sequence of 0 to 
many statements); the return value will be None. It can be 'eval' if the source 
is a single expression; the return value will be the value of the expression. 
It can be 'single' if the source is a single non-empty interactive statement; 
the return value will be None, as with 'exec', but if the statement is an 
expression that evaluates to something other than None, the value will be 
printed.

(#13677 is about changing the doc and docstring for the compile flags argument. 
Patches for that and this should be disjoint.)

The eval(expression, ..) doc say that expression is a string. It much later 
says that it can also be a code object. I think the eval doc should follow the 
exec doc and call the first positional-only arg 'object' and then say the same 
thing: 'object must be either a string or a code object.' I don't have a 
complete suggested revision yet.

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assignee: docs@python
components: Documentation
messages: 200318
nosy: docs@python, terry.reedy
priority: normal
severity: normal
stage: needs patch
status: open
title: Clarify compile and eval interaction.
versions: Python 2.7, Python 3.3, Python 3.4

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