How to call Python functions dynamically

Using global is a very, very, bad way of doing this. You should be doing it this way:

fields = {'name':clean_name,'email':clean_email}

for key in fields:
    fields[key]()

Map your functions to values in a dictionary.

Also using vars()[] is wrong too.

It would be better to have a dictionary of such functions than to look in globals().

The usual approach is to write a class with such functions:

class Cleaner(object):
    def clean_name(self):
        pass

and then use getattr to get access to them:

cleaner = Cleaner()
for f in fields:
    getattr(cleaner, 'clean_%s' % f)()

You could even move further and do something like this:

class Cleaner(object):
    def __init__(self, fields):
        self.fields = fields

    def clean(self):
        for f in self.fields:
            getattr(self, 'clean_%s' % f)()

Then inherit it and declare your clean_<name> methods on an inherited class:

cleaner = Cleaner(['one', 'two'])
cleaner.clean()

Actually this can be extended even further to make it more clean. The first step probably will be adding a check with hasattr() if such method exists in your class.

If don't want to use globals, vars and don't want make a separate module and/or class to encapsulate functions you want to call dynamically, you can call them as the attributes of the current module:

import sys
...
getattr(sys.modules[__name__], "clean_%s" % fieldname)()