How do I execute a statement dynamically in Python?
For ex: assume the value x contains the following expression, (a+b)/2,
a = 1
b = 3
x = (a+b)/2
The value for x will be from a table
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4 Answers
Probably you want eval
#!/usr/bin/env python
a = 1
b = 3
x = "(a+b)/2"
print eval(x)
But it's usually considered a bad practice (click here for a more elaborate and funnier explanation)
Comments
You can do:
a = 1
b = 3
x = '(a+b)/2'
print eval(x)
Note that the value for x is enclosed in quotes as eval requires a string or code object.
Also, perhaps read this to make sure you use it safely (as that can often be a concern and I'm not going to pretend to be an expert in its flaws :) ).
2 Comments
Ned Batchelder
There is no way to use eval safely, that article is wrong. Read Eval Really is Dangerous for details.
RocketDonkey
Haha, yeah, I have actually completely avoided it solely due to reading others' comments on this site (and will continue to do so :) ).
Although python has both "exec()" and "eval()", I believe you wan to use the latter in this case:
>>> a = 1
>>> b = 3
>>> x = "(a + b)/2"
>>> eval(x)
2
Comments
You can use eval, as in
eval(x)
Actually you can use
x=eval('(a+b)/2')
to get the result (eval will return the result of the computation in this case).
