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[3.13] DOCS: Suggest always calling exec with a globals argument and no locals argument (GH-119235) #119239

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gpshead merged 1 commit into from
May 20, 2024
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[3.13] DOCS: Suggest always calling exec with a globals argument and no locals argument (GH-119235) #119239

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DOCS: Suggest always calling exec with a globals argument and no loca… 
…ls argument (GH-119235)

Many users think they want a locals argument for various reasons but they do not
understand that it makes code be treated as a class definition. They do not want
their code treated as a class definition and get surprised. The reason not
to pass locals specifically is that the following code raises a `NameError`:

```py
exec("""
def f():
    print("hi")

f()

def g():
    f()
g()
""", {}, {})
```

The reason not to leave out globals is as follows:

```py
def t():
    exec("""
def f():
    print("hi")

f()

def g():
    f()
g()
    """)
```
(cherry picked from commit 7e1a130)

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>
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@hoodmane @miss-islington
hoodmane authored and miss-islington committed May 20, 2024
commit 9b325a524d9c85fa5dff778972008f5d527a4837
10 changes: 7 additions & 3 deletions Doc/library/functions.rst
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Expand Up @@ -608,9 +608,13 @@ are always available. They are listed here in alphabetical order.
will be used for both the global and the local variables. If *globals* and
*locals* are given, they are used for the global and local variables,
respectively. If provided, *locals* can be any mapping object. Remember
that at the module level, globals and locals are the same dictionary. If exec
gets two separate objects as *globals* and *locals*, the code will be
executed as if it were embedded in a class definition.
that at the module level, globals and locals are the same dictionary.

.. note::

Most users should just pass a *globals* argument and never *locals*.
If exec gets two separate objects as *globals* and *locals*, the code
will be executed as if it were embedded in a class definition.

If the *globals* dictionary does not contain a value for the key
``__builtins__``, a reference to the dictionary of the built-in module
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