lambda is slower than function call in python, why

Question

I think lambda is faster than function call, but after testing, I find out that I am wrong. Function call is definitely faster than lambda call.

Can anybody tell me why

Answer 1

timeit('def a(): return [].extend(range(10)) ;a()') is not calling a(); The call to a() is part of the definition of a:

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             

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If you test the pieces separately, the difference is negligible:

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