Importing module in exec-statement in python

Question

I try to import a module with exec("import __ as tmp") in python:

def prepare(self):
    for modName in self._config.modules.keys():
        print(locals())
        exec("import {} as tmp".format(modName))
        print(locals())
        self._moduleInst[modName] = tmp

Output is:

{'modName': 'time', 'self': <pyo.Server.Server object at 0x000001CA17DFB550>}
{'modName': 'time', 'self': <pyo.Server.Server object at 0x000001CA17DFB550>, 'tmp': <module 'time' (built-in)>}

Traceback (most recent call last):
    File "[...]", line 3, in <module>
        startServer(None)
    File "[...]", line 10, in startServer
        server.prepare()
    File "[...]", line 15, in prepare
        self._moduleInst[modName] = tmp
NameError: name 'tmp' is not defined

I get an NameError exception, cause python cannot find tmp. If I print out all local variables, tmp is defined...

Has anybody an idea what I'm doing wrong? Thank you!

Edit: If I try the same in console it works outside a function, but in a function the same error happends... — user3422533, Nov 12 '17 at 10:40
Possible duplicate of [Behavior of exec function in Python 2 and Python 3](https://stackoverflow.com/questions/15086040/behavior-of-exec-function-in-python-2-and-python-3) — Davis Herring, Oct 28 '18 at 18:04

Chen A. · Answer 1 · 2017-11-12T11:13:25.480

0

You don't declare tmp variable anywhere in your function code:

def prepare(self):
    for modName in self._config.modules.keys():
        print(locals())
        exec("import {} as tmp".format(modName))
        print(locals())
        self._moduleInst[modName] = vars()['tmp']

The tmp in your exec statement is a string. So I guess what you are trying to do is this: self._moduleInst[modName] = 'tmp', which saves the string tmp to your dict.

edited Nov 12 '17 at 11:13

answered Nov 12 '17 at 10:59

Chen A.

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I want to save a reference to the imported module, but in yout solution I "only" save a string, but no module reference. – user3422533 Nov 12 '17 at 11:09
I resolved the problem temp with this solution: self._moduleInst[modName] = locals()["tmp"] – user3422533 Nov 12 '17 at 11:10
If that's the case, you should use vars() to print the dict. I've updated my answer. – Chen A. Nov 12 '17 at 11:13

score 0 · Answer 2 · answered Nov 12 '17 at 14:12

Sorry, I seem unable to reproduce this. My code:

class foo:
    modules = { 'string' : 0 }

    def prepare(self):
        for modName in self.modules.keys():
            print(locals())
            exec("import {} as tmp".format(modName))
            print(locals())
            self.modl = tmp

somevar = foo()
somevar.prepare()
print(somevar.modl.digits)

Output:

{'modName': 'string', 'self': <__main__.foo instance at 0x7f5c11123128>}
{'tmp': <module 'string' from '/usr/lib/python2.7/string.pyc'>, 'modName': 'string', 'self': <__main__.foo instance at 0x7f5c11123128>}
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Difference in Python versions?

I use Python 3.6.2 (v3.6.2:5fd33b5). With Python 2.7 I have no problems. Maybe it's an bug in python..? — user3422533, Nov 12 '17 at 20:58

Importing module in exec-statement in python

2 Answers2