How to call same method for a list of objects

Question

Suppose code like this   class Base      def start self           pass     def stop self          pass  class A Base       def start self               do something for A     def stop self               do something for A  class B Base       def start self        def stop self    a1   A    a2   A   b1   B    b2   B    all    a1  b1  b2  a2          Now I want to call methods start and stop  maybe also others  for each object in the list all  Is there any elegant way for doing this except of writing a bunch of functions like  def start all all       for item in all          item start    def stop all all

User · Answer

Starting in Python 2 6 there is a operator methodcaller function    So you can get something more elegant  and fast    from operator import methodcaller  map methodcaller  method name    list of objects

User · Answer

The   all   functions are so simple that for a few methods I d just write the functions  If you have lots of identical functions  you can write a generic function   def apply on all seq  method   args    kwargs       for obj in seq           getattr obj  method   args    kwargs    Or create a function factory   def create all applier method  doc None       def on all seq   args    kwargs           for obj in seq              getattr obj  method   args    kwargs      on all   doc     doc     return on all  start all   create all applier  start    Start all instances   stop all   create all applier  stop    Stop all instances

User · Answer

Taking  Ants Aasmas answer one step further  you can create a wrapper that takes any method call and forwards it to all elements of a given list   class AllOf      def   init   self  elements           self elements   elements     def   getattr   self  attr           def on all  args    kwargs               for obj in self elements                  getattr obj  attr   args    kwargs          return on all   That class can then be used like this   class Foo      def   init   self  val  quux             self val   val     def foo self           print  foo      self val  a     Foo  foo    Foo  bar    Foo    AllOf a  foo     Which produces the following output   foo  foo foo  bar foo  quux   With some work and ingenuity it could probably be enhanced to handle attributes as well  returning a list of attribute values

User · Answer

It seems like there would be a more Pythonic way of doing this  but I haven t found it yet   I use  map  sometimes if I m calling the same function  not a method  on a bunch of objects   map do something  a list of objects    This replaces a bunch of code that looks like this    do something a   do something b   do something c         But can also be achieved with a pedestrian  for  loop     for obj in a list of objects         do something obj    The downside is that a  you re creating a list as a return value from  map  that s just being throw out and b  it might be more confusing that just the simple loop variant   You could also use a list comprehension  but that s a bit abusive as well  once again  creating a throw-away list        do something x  for x in a list of objects     For methods  I suppose either of these would work  with the same reservations    map lambda x  x method call    a list of objects    or    x method call   for x in a list of objects     So  in reality  I think the pedestrian  yet effective   for  loop is probably your best bet

User · Answer

The approach  for item in all      item start     is simple  easy  readable  and concise  This is the main approach Python provides for this operation  You can certainly encapsulate it in a function if that helps something  Defining a special function for this for general use is likely to be less clear than just writing out the for loop

User · Answer

maybe map  but since you don t want to make a list  you can write your own     def call for all f  seq       for i in seq          f i    then you can do   call for all lamda x  x start    all  call for all lamda x  x stop    all    by the way  all is a built in function  don t overwrite it  -

User · Answer

This will work  all    a1  b1  b2  a2         map lambda x  x start   all        simple example  all     MILK   BREAD   EGGS   map lambda x x lower   all   gt  gt  gt   milk   bread   eggs     and in python3  all     MILK   BREAD   EGGS   list map lambda x x lower   all    gt  gt  gt   milk   bread   eggs

[python] How to call same method for a list of objects?

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