Executing a string

[Heshan Suri]

Hi,
If I execute the following code I will get the the output as 2. What I need is to execute the string str. Is there a way that I can execute the string str as it is, so I will get the output as 5.

def add(a,b):
    return a+b
 
var = 2
str = "var = add(2,3)"
[color=#4080FF]# execute the code snippet inside the str string variable[/color]
print var
 

[Smygis]

>>> expr = "var = (2+3)+pow(2,2)"
>>> exec(expr)
>>> var
9
 

[jlm699]

As smygis silently pointed out, you should not use reserved words for variable declarations...
In your example you used str = 'var = add(2,3)'... but if you wanted to type-cast a numeric variable you would not be able to do str(some_num) ...
It would behoove you to try and avoid this in your python scripts from now on.

[raubana]

It looks like you made the command part of the text:

"a+b = var(a,b)"

instead of

"a+b =", var(a,b)

One thing I'd do is convert the result into a string:

 
def add(a,b):
* * return a+b
 
var = 2
str = "var =" + str( add(2,3) )
[color=#4080FF]# execute the code snippet inside the str string variable[/color]    
 
print var
 
 

That's all there is to it.

[jlm699]

It looks like you made the command part of the text:

"a+b = var(a,b)"

That's what he wanted to do.

Using exec() allows him to take a string and execute it as if the string was a command. This function is extremely helpful when working with a very dynamic program, as it allows you to do things similar to this:

>>> elem1 = 'ab'
>>> elem2 = 'wtf'
>>> elem3 = 'foo'
>>> elem4 = 'bar'
>>> elem5 = 'lol'
>>> elem6 = 'abc'
>>> for idx in range(1, 7):
...     exec('print elem%d' % idx)
...     
ab
wtf
foo
bar
lol
abc
>>> 

Additionally the assignment could be taken care of in the same manner:

txts = ['ab', 'wtf', 'foo', 'bar', 'lawl', 'abc']
for idx in range(1, 7):
    exec( "elem%d = '%s'" % ( idx, txts[idx - 1] ) )
 
for idx in range(1, 7):
    exec( 'print elem%d' % idx )
 
ab
wtf
foo
bar
lawl
abc