clarification needed on exec usage in python

Question

I have this:

>>> d = {}
>>> d["hi"] = 12345

>>> d1 = {}

>>> d1["hiiii"] = 1234590

I know why I get an error below. This is because exec could not find variables hi and hiiii.

>>> exec "print hi, hiiii"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1, in <module>
NameError: name 'hi' is not defined


>>> exec "print hiiii"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 1, in <module>
NameError: name 'hiiii' is not defined

Now it works because exec was able to find hi and hiiii variables in dictionary d and d1

>>> exec "print hi, hiiii" in d , d1
12345 1234590

So far so good.

Question:

Now when I print d I see that it has been modified and prints lot of key,value pairs..why? But on printing d1 I do not see lot of key,value pairs, why so?

Chronial · Accepted Answer · 2013-09-10 23:59:42Z

3

This is explained in the docs:

As a side effect, an implementation may insert additional keys into the dictionaries given besides those corresponding to variable names set by the executed code. For example, the current implementation may add a reference to the dictionary of the built-in module __builtin__ under the key __builtins__ (!).

answered Sep 10, 2013 at 23:59

Chronial

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