Python eval example code

Python eval evaluate expression, not statement. Let's see a example

 
v=5
print v
v=eval("v+5")
print v
#eval("print v") #It will not work

Output:

5
10

Python dynamically add class attribute

Dynamically add attribute of a class is very easy in python. And it is useful to know.
Here I have a class named Arithmetic, now I want to add functionality of this class named addNum which perform add two number.
Lets see the example

 
class Arithmetic(object):
    pass

def arithmetic_function_add(cls):
    def sampleFunction(self,a,b):
        return a+b
    sampleFunction.__name__ = "addNum"
    setattr(cls,sampleFunction.__name__,sampleFunction)

arithmetic_function_add(Arithmetic)

arithmetic=Arithmetic()
print arithmetic.addNum(5,6)

Output:

11

python dynamic code execution, exec exaqmple

Dynamic code execution is very important in some cases. Sometimes we need to generate code dynamically and then run it. Lets see a very simple example using exec:

 
v=5

code = """def myFun():
            global v
            v=10
            print 'This is my function'
       """
exec code

print v
myFun() #must execute the code before calling function
print v

Output:

5
This is my function
10