I have a variable with a string assigned to it and I want to define a new variable based on that string.
foo = "bar"
foo = "something else"
# What I actually want is:
bar = "something else"
3 Answers
You can use exec for that:
>>> foo = "bar"
>>> exec(foo + " = 'something else'")
>>> print bar
something else
>>>
9 Comments
mgalgs
+1 because he answered the question (as bad an idea as it may be).
Clock ZHONG
@mgalgs why it's a bad idea? Any bad effect this solution have? Thanks in advance.
jpp
Note use of
exec / eval is considered poor practice. I have not met a single use case where it has been helpful, and there are usually better alternatives such as dict.
niCk cAMel
why doesn't this work when used in pytest unittests?
Olshansky
+100 what @jpp said. While this answer is useful and correct, if you're writing something other than a one-off script, you can most likely use a
dict. |
You will be much happier using a dictionary instead:
my_data = {}
foo = "hello"
my_data[foo] = "goodbye"
assert my_data["hello"] == "goodbye"
7 Comments
dnsmkl
It does not seem to address the question.
sudo
Yes. This may be helpful, but it wasn't what the OP was asking.
Ned Batchelder
I'm glad to see the answer is still here. I think we can trust Stack Overflow readers to judge for themselves whether an answer suits their needs. This answer does not provide "variable variables," it is true. But I guarantee you that 99% of the people looking for them will be happier to have found dictionaries.
Berto 'd Sera
It does not DIRECTLY answer the question, however, people might be asking that question while ignoring they can use a dictionary for the same purpose
Ned Batchelder
"I'm cold, how can I set my house on fire?"
|
You can use setattr
name = 'varname'
value = 'something'
setattr(self, name, value) #equivalent to: self.varname= 'something'
print (self.varname)
#will print 'something'
But, since you should inform an object to receive the new variable, this only works inside classes or modules.
3 Comments
sudo
Correct, it only works inside classes.
Demis
Can this be used inside Modules, so set a module-level attribute? Eg.
MyModule.varDemis
To answer my own question, yes, it can be used from within a module, on itself: stackoverflow.com/questions/2933470/…
execis becauselocals()doesn't support modifications.locals()doesn't support modifications because it would make the implementation more complex and slower and is never a good idea