append new row to old csv file python

Question

I am trying to add a new row to my old csv file  Basically  it gets updated each time I run the Python script    Right now I am storing the old csv rows values in a list and then deleting the csv file and creating it again with the new list value   Wanted to know are there any better ways of doing this

User · Answer

Are you opening the file with mode of  a  instead of  w   See Reading and Writing Files in the python docs  7 2  Reading and Writing Files open   returns a file object  and is most commonly used with two arguments  open filename  mode    gt  gt  gt  f   open  workfile    w    gt  gt  gt  print f  lt open file  workfile   mode  w  at 80a0960 gt   The first argument is a string containing the filename  The second argument is another string containing a few characters describing the way in which the file will be used  mode can be  r  when the file will only be read   w  for only writing  an existing file with the same name will be erased   and  a  opens the file for appending  any data written to the file is automatically added to the end   r   opens the file for both reading and writing  The mode argument is optional   r  will be assumed if it   s omitted  On Windows   b  appended to the mode opens the file in binary mode  so there are also modes like  rb    wb   and  r b   Python on Windows makes a distinction between text and binary files  the end-of-line characters in text files are automatically altered slightly when data is read or written  This behind-the-scenes modification to file data is fine for ASCII text files  but it   ll corrupt binary data like that in JPEG or EXE files  Be very careful to use binary mode when reading and writing such files  On Unix  it doesn   t hurt to append a  b  to the mode  so you can use it platform-independently for all binary files

User · Answer

I prefer this solution using the csv module from the standard library and the with statement to avoid leaving the file open   The key point is using  a  for appending when you open the file   import csv    fields   first   second   third   with open r name    a   as f      writer   csv writer f      writer writerow fields    If you are using Python 2 7 you may experience superfluous new lines in Windows  You can try to avoid them using  ab  instead of  a  this will  however  cause you TypeError  a bytes-like object is required  not   39 str  39  in python and CSV in Python 3 6  Adding the newline     as Natacha suggests  will cause you a backward incompatibility between Python 2 and 3

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Based in the answer of  G M and paying attention to the  John La Rooy s warning  I was able to append a new row opening the file in  a mode      Even in windows  in order to avoid the newline problem  you must declare it as newline          Now you can open the file in  a mode  without the b     import csv  with open r names csv    a   newline     as csvfile      fieldnames     This   aNew       writer   csv DictWriter csvfile  fieldnames fieldnames       writer writerow   This   is    aNew   Row      I didn t try with the regular writer  without the Dict   but I think that it ll be ok too

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I like using the codecs opening in a with  field names     latitude    longitude    date    user    text   with codecs open filename  ab   encoding  utf-8   as logfile      logger   csv DictWriter logfile  fieldnames field names      logger writeheader      some more code stuff       for video in aList          video result                                                   video result  date     video  snippet    publishedAt           video result  user     video  id           video result  text     video  snippet    description   encode  utf8           logger writerow video result

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with open  document csv   a   as fd      fd write myCsvRow    Opening a file with the  a  parameter allows you to append to the end of the file instead of simply overwriting the existing content  Try that

User · Answer

If you use pandas  you can append your dataframes to an existing CSV file this way  df to csv  log csv   mode  a   index False  header False   With mode  a  we ensure that we append  rather than overwrite  and with header False we ensure that we append only the values of df rows  rather than header   values

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I follow this way to append a new line in a  csv file  pose x   1  pose y   2  with open  path-to-your-csv-file csv   mode  a   as file       file  write  quot       quot  format pose x  pose y       file  write  quot  n quot

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If the file exists and contains data  then it is possible to generate the fieldname parameter for csv DictWriter automatically     read header automatically with open myFile   r   as f      reader   csv reader f      for header in reader          break    add row to CSV file with open myFile   a   newline     as f      writer   csv DictWriter f  fieldnames header      writer writerow myDict

[python] append new row to old csv file python

7.2. Reading and Writing Files

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