how to pass parameters of a function when using timeit.Timer()

The functions can use arguments in timeit if these are created using closures, we can add this behaviours by wrapping them in another function.

def foo(num1, num2):
    def _foo():
        # do something to num1 and num2
        pass
    return _foo

A = 1
B = 2

import timeit
t = timeit.Timer(foo(A,B))  
print(t.timeit(5))

or shorter, we can use functools.partial instead of explicit closures declaration

def foo(num1, num2):
    # do something to num1 and num2
    pass

A = 1
B = 2

import timeit, functools
t = timeit.Timer(functools.partial(foo, A, B)) 
print(t.timeit(5))

EDIT using lambda, thanks @jupiterbjy

we can use lambda function without parameters instead of functools library

def foo(num1, num2):
    # do something to num1 and num2
    pass

A = 1
B = 2

import timeit
t = timeit.Timer(lambda: foo(A, B)) 
print (t.timeit(5))

The code snippets must be self-contained - they cannot make external references. You must define your values in the statement-string or setup-string:

import timeit

setup = """
A = 1
B = 2

def foo(num1, num2):
    pass

def mainprog():
    global A,B
    for i in range(20):
        # do something to A and B
        foo(A, B)
"""

t = timeit.Timer(stmt="mainprog()" setup=setup)
print(t.timeit(5))

Better yet, rewrite your code to not use global values.