Skip first entry in for loop in python

Question

In python  How do I do something like   for car in cars       Skip first and last  do work for rest

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Based on  SvenMarnach  s Answer  but bit simpler and without using deque   gt  gt  gt  def skip iterable  at start 0  at end 0       it   iter iterable      it   itertools islice it  at start  None      it  it1   itertools tee it      it1   itertools islice it1  at end  None      return  next it  for   in it1    gt  gt  gt  list skip range 10   at start 2  at end 2    2  3  4  5  6  7   gt  gt  gt  list skip range 10   at start 2  at end 5    2  3  4    Also Note  based on my timeit result  this is marginally faster than the deque solution   gt  gt  gt  iterable xrange 1000   gt  gt  gt  stmt1     def skip iterable  at start 0  at end 0       it   iter iterable      it   itertools islice it  at start  None      it  it1   itertools tee it      it1   itertools islice it1  at end  None      return  next it  for   in it1  list skip iterable 2 2            gt  gt  gt  stmt2     def skip iterable  at start 0  at end 0       it   iter iterable      for x in itertools islice it  at start           pass     queue   collections deque itertools islice it  at end       for x in it          queue append x          yield queue popleft   list skip iterable 2 2                gt  gt  gt  timeit timeit stmt   stmt1  setup  from   main   import iterable  skip  itertools   number   10000  2 0313770640908047  gt  gt  gt  timeit timeit stmt   stmt2  setup  from   main   import iterable  skip  itertools  collections   number   10000  2 9903135454296716

User · Answer

An alternative method   for idx  car in enumerate cars         Skip first line      if not idx          continue       Skip last line      if idx   1    len cars           continue       Real code here      print car

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for item in do not use list as a name 1 -1           do whatever

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Example  mylist   one   two   three   four   five   for i in mylist 1       print i   In python index start from 0  We can use  slicing operator to make manipulations in iteration  for i in range 1 -1

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Here is a more general generator function that skips any number of items from the beginning and end of an iterable   def skip iterable  at start 0  at end 0       it   iter iterable      for x in itertools islice it  at start           pass     queue   collections deque itertools islice it  at end       for x in it          queue append x          yield queue popleft     Example usage    gt  gt  gt  list skip range 10   at start 2  at end 2    2  3  4  5  6  7

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The best way to skip the first item s  is   from itertools import islice for car in islice cars  1  None         do something   islice in this case is invoked with a start-point of 1  and an end point of None  signifying the end of the iterator   To be able to skip items from the end of an iterable  you need to know its length  always possible for a list  but not necessarily for everything you can iterate on   for example  islice cars  1  len cars -1  will skip the first and last items in the cars list

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The other answers only work for a sequence   For any iterable  to skip the first item   itercars   iter cars  next itercars  for car in itercars        do work   If you want to skip the last  you could do   itercars   iter cars    add  next itercars   here if you also want to skip the first prev   next itercars  for car in itercars        do work on  prev  not  car        at end of loop      prev   car   now you can do whatever you want to do to the last one on  prev

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Well  your syntax isn t really Python to begin with   Iterations in Python are over he contents of containers  well  technically it s over iterators   with a syntax for item in container  In this case  the container is the cars list  but you want to skip the first and last elements  so that means cars 1 -1   python lists are zero-based  negative numbers count from the end  and   is slicing syntax   So you want   for c in cars 1 -1       do something with c

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To skip the first element in Python you can simply write  for car in cars 1          Do What Ever you want   or to skip the last elem  for car in cars  -1         Do What Ever you want   You can use this concept for any sequence

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The more itertools project extends itertools islice to handle negative indices   Example  import more itertools as mit  iterable    ABCDEFGH  list mit islice extended iterable  1  -1     Out    B    C    D    E    F    G     Therefore  you can elegantly apply it slice elements between the first and last items of an iterable   for car in mit islice extended cars  1  -1         do something

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I do it like this  even though it looks like a hack it works every time   ls of things     apple    car    truck    bike    banana   first   0 last   len ls of things  for items in ls of things      if first    0         first   first   1         pass     elif first    last - 1          break     else          do stuff         first   first   1         pass

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If cars is a sequence you can just do   for car in cars 1 -1       pass

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Here s my preferred choice  It doesn t require adding on much to the loop  and uses nothing but built in tools   Go from   for item in my items    do something item    to   for i  item in enumerate my items     if i    0      continue   do something item

[python] Skip first entry in for loop in python?

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