python - A decorator which converts string to number -

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• can't modify list elements in loop python [duplicate] 5 answers

i use decorators convert numbers in string format int/float value, here how trying it

def str_to_int(func):      """         wrapper converts string value integer      """      def wrapper(*args, **kwargs):          arg in args:              arg = int(arg)          return func(*args, **kwargs)      return wrapper  @str_to_int  def number_as_string(a, b, c):      return a,b,c  print (number_as_string('1', '2', '3')) 

output

('1', '2', '3') 

however, wanted below

(1, 2, 3) 

the above output generate below code

def str_to_int(func):      """         wrapper converts string value integer      """      def wrapper(x, y, z):          return int(x), int(y), int(z)      return wrapper  @str_to_int  def number_as_string(a, b, c):      return a,b,c  print (number_as_string('1', '2', '3')) 

but above code defeats purpose of using decorator @ first place, since convert string values irrespective of arguments original function has.

could 1 suggest wrong first program , how resolve it.

the reason not working expected because never update incoming args, keep overwriting value in loop.

consider revised version:

>>> def str_to_int(f): ...   def wrapper(*args, **kwargs): ...     args = map(int, args) ...     return f(*args, **kwargs) ...   return wrapper ... >>> @str_to_int ... def foo(a,b,c): ...   return a,b,c ... >>> foo('1','2','3') (1, 2, 3) 

the key list line:

args = map(int, args) 

it makes sure original args tuple replaced completely, in loop silently discarding value.

for python3, should use:

args = tuple(map(int, args)) 

as map return map object.

of course hope realize decorator works if pass things can converted numbers, if pass in string raise valueerror:

>>> foo('hello') traceback (most recent call last):   file "<stdin>", line 1, in <module>   file "<stdin>", line 3, in wrapper valueerror: invalid literal int() base 10: 'hello' 

if want prevent that, have ignore values cannot converted integer:

def wrapper(*args, **kwargs):    _temp = []    in args:      try:        _temp.append(int(i))      except valueerror:        _temp.append(i)    args = tuple(_temp)    return f(*args, **kwargs) 

now ignore things cannot convert:

>>> foo('hello', '1', '2') ('hello', 1, 2) 

you can shorten code bit, * automatically expand arguments, can use advantage:

 # args = tuple(_temp)  return f(*_temp, **kwargs)