What is the difference between json dump and json dumps in python

Question

I searched in this official document to find difference between the json dump   and json dumps   in python  It is clear that they are related with file write option  But what is the detailed difference between them and in what situations one has more advantage than other

User · Answer

In memory usage and speed   When you call jsonstr   json dumps mydata  it first creates a full copy of your data in memory and only then you file write jsonstr  it to disk  So this is a faster method but can be a problem if you have a big piece of data to save   When you call json dump mydata  file  -- without  s   new memory is not used  as the data is dumped by chunks  But the whole process is about 2 times slower   Source  I checked the source code of json dump   and json dumps   and also tested both the variants measuring the time with time time   and watching the memory usage in htop

User · Answer

The functions with an s take string parameters  The others take file  streams

User · Answer

One notable difference in Python 2 is that if you re using ensure ascii False  dump will properly write UTF-8 encoded data into the file  unless you used 8-bit strings with extended characters that are not UTF-8    dumps on the other hand  with ensure ascii False can produce a str or unicode just depending on what types you used for strings      Serialize obj to a JSON formatted str using this conversion table  If ensure ascii is False  the result may contain non-ASCII characters and the return value may be a unicode instance     emphasis mine   Note that it may still be a str instance as well   Thus you cannot use its return value to save the structure into file without checking which  format was returned and possibly playing with unicode encode   This of course is not valid concern in Python 3 any more  since there is no more this 8-bit Unicode confusion     As for load vs loads  load considers the whole file to be one JSON document  so you cannot use it to read multiple newline limited JSON documents from a single file

User · Answer

There isn t much else to add other than what the docs say  If you want to dump the JSON into a file socket or whatever  then you should go with dump    If you only need it as a string  for printing  parsing or whatever  then use dumps    dump string  As mentioned by Antti Haapala in this answer  there are some minor differences on the ensure ascii behaviour  This is mostly due to how the underlying write   function works  being that it operates on chunks rather than the whole string  Check his answer for more details on that  json dump    Serialize obj as a JSON formatted stream to fp  a  write  -supporting file-like object If ensure ascii is False  some chunks written to fp may be unicode instances  json dumps    Serialize obj to a JSON formatted str If ensure ascii is False  the result may contain non-ASCII characters and the return value may be a unicode instance

[python] What is the difference between json.dump() and json.dumps() in python?

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