Is it possible to “dynamically” create local variables in Python? [duplicate]

Question

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• Dynamically set local variable [duplicate] 7 answers

Is it possible to create a local variables with Python code, given only the variable's name (a string), so that subsequent calls to "'xxx' in locals()" will return True?

Here's a visual :

>>> 'iWantAVariableWithThisName' in locals()
False
>>> junkVar = 'iWantAVariableWithThisName'
>>> (...some magical code...)
>>> 'iWantAVariableWithThisName' in locals()
True

For what purpose I require this trickery is another topic entirely...

Thanks for the help.

Answer 1

If you really want to do this, you could use exec:

print 'iWantAVariableWithThisName' in locals()
junkVar = 'iWantAVariableWithThisName'
exec(junkVar + " = 1")
print 'iWantAVariableWithThisName' in locals()

Of course, anyone will tell you how dangerous and hackish using exec is, but then so will be any implementation of this "trickery."

Answer 2

You can play games and update locals() manually, which will sometimes work, but you shouldn't. It's specifically warned against in the docs. If I had to do this, I'd probably use exec:

>>> 'iWantAVariableWithThisName' in locals()
False
>>> junkVar = 'iWantAVariableWithThisName'
>>> exec(junkVar + '= None')
>>> 'iWantAVariableWithThisName' in locals()
True
>>> print iWantAVariableWithThisName
None

But ninety-three times out of one hundred you really want to use a dictionary instead.

Answer 3

No need to use exec, but locals()[string], or vars() or globals() also work.

test1="Inited"

if not "test1" in locals(): locals()["test1"] = "Changed"
if not "test1" in locals(): locals()["test2"] = "Changed"

print " test1= ",test1,"\n test2=",test2