CODEWITHSUNDEEP
pythonpython-3.x
Dedi
Dedi

Reputation: 35

Difference between "None" end "pass" in a try/except statement in terms of calculation time

I'm using and try/except statement in python inside a very long loop. If the exception is raised, it should do nothing.

try :
  *Some Code*
except :
  pass

If i use this first proposition, the total time of calculation for the loop is about 10 minutes.

try :
  *Some Code*
except :
  None

If i use this second propositon, the total time of calculation for the loop is about 2 minutes.

Why is it so different, and why is the second one faster as, logically for me, pass is a better solution than None ?

The exact code is :

try:
 indexes = peakutils.peak.interpolate(self.list_height, input_1, ind=indexes, width=self.gauss_width)
except:
 None / Pass

I made several tests with both propisitons and it's always the same.

How time is calculated : 

start = default_timer()
im.get_events() #The loop where the try/except statement appears
finish = default_timer()
print('ELAPSED TIME : %s'%(finish - start))

Upvotes: 0

Views: 582

Answers (1)

Kruupös
Kruupös

Reputation: 5474

Given two functions:

def func_none():
  return None

def func_pass():
  pass

They are doing exactly the same thing, the proof using dis:

>>> import dis
>>> dis.dis(func_none)
# 0 LOAD_CONST               0 (None)
# 3 RETURN_VALUE

>>> dis.dis(func_pass)
# 0 LOAD_CONST               0 (None)
# 3 RETURN_VALUE

Indeed, here is the definition of pass:

pass is a null operation — when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed, for example:

Conclusion: pass statement is as fast as Nonein theory.

Edit: why it may be a slower time using None instead of return None (like in OP example).

Given two functions:

def func_none():
  try:
    1/0
  except:
    None

def func_pass():
  try:
    1/0
  except:
    pass

The difference using dis:

>>> import dis
>>> dis.dis(func_none)
# Skip to expect part

  18 LOAD_CONST               0 (None)
  21 POP_TOP             
  22 JUMP_FORWARD             1 (to 26)
  25 END_FINALLY         
  26 LOAD_CONST               0 (None)
  29 RETURN_VALUE  

dis.dis(func_pass)

# Skip to expect part

  18 JUMP_FORWARD             1 (to 22)
  21 END_FINALLY         
  22 LOAD_CONST               0 (None)
  25 RETURN_VALUE

So it is clear that using None instead of pass will add two extra operation LOAD_CONST and POP_TOP. It shouldnt add 8 minutes though, so I'm sure this isn't the real reason.

Upvotes: 3

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