Writing a Python list of lists to a csv file

Question

I have a long list of lists of the following form ---  a     1 2  abc  3   1 2  werew  4            1 4  qew  2     i e  the values in the list are of different types -- float int  strings How do I write it into a csv file so that my output csv file looks like  1 2 abc 3 1 2 werew 4       1 4 qew 2

User · Answer

I got an error message when following the examples with a newline parameter in the csv writer function  The following code worked for me     with open strFileName   w   as f      writer   csv writer f  delimiter       quoting csv QUOTE MINIMAL      writer writerows result

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In case of exporting lll list of lists of lists to  csv  this will work in Python3  import csv with open  quot output csv quot    quot w quot   as f      writer   csv writer f      for element in lll          writer writerows element

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If for whatever reason you wanted to do it manually  without using a module like csv pandas numpy etc     with open  myfile csv   w   as f      for sublist in mylist          for item in sublist              f write item                f write   n     Of course  rolling your own version can be error-prone and inefficient     that s usually why there s a module for that  But sometimes writing your own can help you understand how they work  and sometimes it s just easier

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Make sure to indicate lineterinator   n  when create the writer  otherwise  an extra empty line might be written into file after each data line when data sources are from other csv file     Here is my solution   with open  csvfile    a   as csvfile      spamwriter   csv writer csvfile  delimiter        quotechar      quoting csv QUOTE MINIMAL  lineterminator   n   for i in range 0  len data        spamwriter writerow data i

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If you don t want to import csv module for that  you can write a list of lists to a csv file using only Python built-ins  with open  output csv    w   as f      for row in a          f write   s n        join str col  for col in row

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How about dumping the list of list into pickle and restoring it with pickle module  It s quite convenient     gt  gt  gt  import pickle  gt  gt  gt    gt  gt  gt  mylist    1   foo    bar    1  2  3      1 4 2 6    3 6 0 10     gt  gt  gt  with open  mylist    wb   as f          pickle dump mylist  f      gt  gt  gt  with open  mylist    rb   as f           mylist   pickle load f   gt  gt  gt  mylist  1   foo    bar    1  2  3     1  4  2  6    3  6  0  10     gt  gt  gt

User · Answer

Python s built-in CSV module can handle this easily   import csv  with open  output csv    wb   as f      writer   csv writer f      writer writerows a    This assumes your list is defined as a  as it is in your question  You can tweak the exact format of the output CSV via the various optional parameters to csv writer   as documented in the library reference page linked above   Update for Python 3  import csv  with open  out csv    w   newline     as f      writer   csv writer f      writer writerows a

User · Answer

You could use pandas   In  1   import pandas as pd  In  2   a     1 2  abc  3   1 2  werew  4   1 4  qew  2    In  3   my df   pd DataFrame a   In  4   my df to csv  my csv csv   index False  header False

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import csv with open file path   a   as outcsv          configure writer to write standard csv file     writer   csv writer outcsv  delimiter      quotechar      quoting csv QUOTE MINIMAL  lineterminator   n       writer writerow   number    text    number        for item in list           Write item to outcsv         writer writerow  item 0   item 1   item 2      official docs  http   docs python org 2 library csv html

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Ambers s solution also works well for numpy arrays   from pylab import   import csv  array  arange 0 10 1  list   array  array  2 array  3  with open  output csv    wb   as f      writer   csv writer f      writer writerows list

User · Answer

Using csv writer in my very large list took quite a time  I decided to use pandas  it was faster and more easy to control and understand    import pandas   yourlist                      pd   pandas DataFrame yourlist   pd to csv  mylist csv     The good part you can change somethings to make a better csv file    yourlist                      columns     abcd   bcde   cdef    a csv with 3 columns  index    i 0  for i in yourlist   first element of every list in yourlist  not index list    i 1   for i in yourlist   pd   pandas DataFrame not index list  columns   columns  index   index     Now you have a csv with columns and index   pd to csv  mylist csv

[python] Writing a Python list of lists to a csv file

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