Apply function to each element of a list

Question

How do I apply a function to the list of variable inputs  For e g  the filter function returns true values but not the actual output of the function   from string import upper mylis   this is test    another test    filter upper  mylis    this is test    another test     The expected output is      THIS IS TEST    ANOTHER TEST     I know upper is built-in  This is just an example

User · Accepted Answer

I think you mean to use map instead of filter    gt  gt  gt  from string import upper  gt  gt  gt  mylis   this is test    another test    gt  gt  gt  map upper  mylis    THIS IS TEST    ANOTHER TEST     Even simpler  you could use str upper instead of importing from string  thanks to  alecxe     gt  gt  gt  map str upper  mylis    THIS IS TEST    ANOTHER TEST     In Python 2 x  map constructs a new list by applying a given function to every element in a list  filter constructs a new list by restricting to elements that evaluate to True with a given function   In Python 3 x  map and filter construct iterators instead of lists  so if you are using Python 3 x and require a list the list comprehension approach would be better suited

User · Answer

Sometimes you need to apply a function to the members of a list in place  The following code worked for me   gt  gt  gt  def func a  i           a i    a i  lower    gt  gt  gt  a     TEST    TEXT    gt  gt  gt  list map lambda i func a  i   range 0  len a      None  None   gt  gt  gt  print a    test    text    Please note  the output of map   is passed to the list constructor to ensure the list is converted in Python 3  The returned list filled with None values should be ignored  since our purpose was to convert list a in place

User · Answer

Or  alternatively  you can take a list comprehension approach    gt  gt  gt  mylis     this is test    another test    gt  gt  gt   item upper   for item in mylis    THIS IS TEST    ANOTHER TEST

[python] Apply function to each element of a list

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