Is there a better way to iterate over two lists getting one element from each list for each iteration

Question

I have a list of Latitudes and one of Longitudes and need to iterate over the latitude and longitude pairs   Is it better to    A  Assume that the lists are of equal lengths   for i in range len Latitudes        Lat Long  Latitudes i  Longitudes i    B  Or   for Lat Long in   x y  for x in Latitudes for y in Longitudes       Note that B is incorrect  This gives me all the pairs  equivalent to itertools product     Any thoughts on the relative merits of each  or which is more pythonic

User · Answer

Another way to do this would be to by using map.

>>> a
[1, 2, 3]
>>> b
[4, 5, 6]
>>> for i,j in map(None,a,b):
    ...   print i,j
    ...
1 4
2 5
3 6

One difference in using map compared to zip is, with zip the length of new list is
same as the length of shortest list. For example:

>>> a
[1, 2, 3, 9]
>>> b
[4, 5, 6]
>>> for i,j in zip(a,b):
    ...   print i,j
    ...
1 4
2 5
3 6

Using map on same data:

>>> for i,j in map(None,a,b):
    ...   print i,j
    ...

    1 4
    2 5
    3 6
    9 None

User · Answer

Good to see lots of love for zip in the answers here    However it should be noted that if you are using a python version before 3 0  the itertools module in the standard library contains an izip function which returns an iterable  which is more appropriate in this case  especially if your list of latt longs is quite long    In python 3 and later zip behaves like izip

User · Answer

This post helped me with zip    I know I m a few years late  but I still want to contribute   This is in Python 3   Note  in python 2 x  zip   returns a list of tuples  in Python 3 x  zip   returns an iterator  itertools izip   in python 2 x    zip   in python 3 x  Since it looks like you re building a list of tuples  the following code is the most pythonic way of trying to accomplish what you are doing    gt  gt  gt  lat    1  2  3   gt  gt  gt  long    4  5  6   gt  gt  gt  tuple list   list zip lat  long    gt  gt  gt  tuple list   1  4    2  5    3  6     Or  alternatively  you can use list comprehensions  or list comps  should you need more complicated operations   List comprehensions also run about as fast as map    give or take a few nanoseconds  and are becoming the new norm for what is considered Pythonic versus map      gt  gt  gt  lat    1  2  3   gt  gt  gt  long    4  5  6   gt  gt  gt  tuple list     x y  for x y in zip lat  long    gt  gt  gt  tuple list   1  4    2  5    3  6    gt  gt  gt  added tuples    x y for x y in zip lat  long    gt  gt  gt  added tuples  5  7  9

User · Answer

for Lat Long in zip Latitudes  Longitudes

User · Answer

Iterating through elements of two lists simultaneously is known as zipping  and python provides a built in function for it  which is documented here    gt  gt  gt  x    1  2  3   gt  gt  gt  y    4  5  6   gt  gt  gt  zipped   zip x  y   gt  gt  gt  zipped   1  4    2  5    3  6    gt  gt  gt  x2  y2   zip  zipped   gt  gt  gt  x    list x2  and y    list y2  True    Example is taken from pydocs   In your case  it will be simply   for  lat  lon  in zip latitudes  longitudes           process lat and lon

User · Answer

in case your Latitude and Longitude lists are large and lazily loaded   from itertools import izip for lat  lon in izip latitudes  longitudes       process lat  lon    or if you want to avoid the for-loop  from itertools import izip  imap out   imap process  izip latitudes  longitudes

User · Answer

This is as pythonic as you can get  for lat  long in zip Latitudes  Longitudes       print lat  long

[python] Is there a better way to iterate over two lists, getting one element from each list for each iteration?

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