[New-bugs-announce] [issue19290] Clarify compile and eval interaction.

Terry J. Reedy report at bugs.python.org
Sat Oct 19 00:25:32 CEST 2013

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.

assignee: docs at python
components: Documentation
messages: 200318
nosy: docs at 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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