>>> timeit('def a():return 222*333 ;a()')
0.08195090293884277
>>> timeit('a=lambda:222*333 ;a()')
0.11071300506591797

>>> timeit('a=lambda: [].extend(range(10)) ;a()')
0.40241098403930664
>>> timeit('a=lambda: [].extend(range(10)) ;a()')
0.4011270999908447
>>> timeit('a=lambda: [].extend(range(10)) ;a()')
0.4064619541168213
>>> timeit('def a(): return [].extend(range(10)) ;a()')
0.07965493202209473
>>> timeit('def a(): return [].extend(range(10)) ;a()')
0.08039593696594238
>>> timeit('def a(): return [].extend(range(10)) ;a()')
0.08103609085083008
>>> timeit('def a(): return [].extend(range(10)) ;a()')
0.08639097213745117

>>> timeit('a()', setup="def a():return 222*333")
0.07061290740966797
>>> timeit('a()', setup="a=lambda: 222*333")
0.06967616081237793

In [34]: def a(): return [].extend(range(10)) ;a()

In [35]: import dis

In [36]: dis.dis(a)
  1           0 BUILD_LIST               0
              3 LOAD_ATTR                0 (extend)
              6 LOAD_GLOBAL              1 (range)
              9 LOAD_CONST               1 (10)
             12 CALL_FUNCTION            1
             15 CALL_FUNCTION            1
             18 RETURN_VALUE
             19 LOAD_GLOBAL              2 (a)
             22 CALL_FUNCTION            0       #<-- a is called
             25 POP_TOP

In [24]: %timeit a=lambda: [].extend(range(10))
10000000 loops, best of 3: 68.6 ns per loop

In [25]: %timeit def a2(): return [].extend(range(10))
10000000 loops, best of 3: 68.8 ns per loop

In [22]: %timeit a()
1000000 loops, best of 3: 445 ns per loop

In [23]: %timeit a2()
1000000 loops, best of 3: 442 ns per loop

def a(): return 10
b = lambda: 10

import dis

>>> dis.dis(a)
1           0 LOAD_CONST               1 (10)
            3 RETURN_VALUE
>>> dis.dis(b)
1           0 LOAD_CONST               1 (10)
            3 RETURN_VALUE

import timeit

def a():
    return 222*333

b = lambda: 222*333

>>> min(timeit.repeat(a))
0.08302917300898116
>>> min(timeit.repeat(b))
0.08061711701157037

import timeit

def a():
    return 222*333

b = lambda: 222*333

setup = 'from __main__ import a, b'

min(timeit.repeat('a()', setup))

0.1410999298095703

min(timeit.repeat('b()', setup))

0.11270594596862793