python - Using builtin __import__() in normal cases -


here checked performance of __import__()

in [9]: %%timeit    ...: math = __import__('math')    ...: sqrt = math.sqrt    ...: sqrt(7894561230)    ...:  slowest run took 11.16 times longer fastest. mean intermediate result being cached. 1000000 loops, best of 3: 534 ns per loop  in [10]: %%timeit     ...: math import sqrt     ...: sqrt(7894561230)     ...:      ...:  slowest run took 10.23 times longer fastest. mean intermediate result being cached. 1000000 loops, best of 3: 979 ns per loop

builtin __import__ module seems faster traditional way import,

so can used in code have used it, or there major harm in doing this, __import__ doc doesn't state harm in doing this.

but states

direct use of __import__() rare, except in cases want import module name known @ runtime.

so question can used in normal cases too. or there disadvantage of ?

here small "benchmark". let's define 2 functions:

def f1():     import sys  def f2():     sys = __import__('sys')

bytecode comparison:

>>> dis.dis(f1)   5           0 load_const               1 (0)               2 load_const               0 (none)               4 import_name              0 (sys)               6 store_fast               0 (sys)               8 load_const               0 (none)              10 return_value  >>> dis.dis(f2)   8           0 load_global              0 (__import__)               2 load_const               1 ('sys')               4 call_function            1               6 store_fast               0 (sys)               8 load_const               0 (none)              10 return_value

the generated bytecodes have same number of instructions, different. timing?

>>> timeit.timeit(f1) 0.4096750088112782  >>> timeit.timeit(f2) 0.474958091968411

it turns out __import__ way slower. in addition, far less readable classical import statement.

conclusion: stick import.

now bit of interpretation...

i suppose calling __import__ slower executing import statement, because bytecode generated latter optimised.

take @ instructions: bytecode __import__ other function call, call_function instruction. on other hand, import statement results in import_name instruction, definetely looks dedicated imports, , executed in optimised way interpreter.

as matter of fact, third instruction true difference between 2 bytecodes. difference between 2 functions lies in difference between import_name , call_function.


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