sprintf like functionality in Python

Question

I would like to create a string buffer to do lots of processing  format and finally write the buffer in a text file using a C-style sprintf functionality in Python  Because of conditional statements  I can   t write them directly to the file   e g pseudo code   sprintf buf  A    d n   B   s n  A B     some processing    sprint buf  C  d n  c           fprintf file buf    So in the output file we have this kind of o p   A  foo B  bar C  ded etc      Edit  to clarify my question  buf is a big buffer contains all these strings which have formatted using sprintf  Going by your examples  buf will only contain current values  not older ones  e g first in buf I wrote A  something  B  something later C  something was appended in the same buf  but in your Python answers buf contains only last value  which is not I want - I want buf to have all the printfs I have done since the beginning  like in C

User · Answer

This is probably the closest translation from your C code to Python code.

A = 1
B = "hello"
buf = "A = %d\n , B= %s\n" % (A, B)

c = 2
buf += "C=%d\n" % c

f = open('output.txt', 'w')
print >> f, c
f.close()

The % operator in Python does almost exactly the same thing as C's sprintf. You can also print the string to a file directly. If there are lots of these string formatted stringlets involved, it might be wise to use a StringIO object to speed up processing time.

So instead of doing +=, do this:

import cStringIO
buf = cStringIO.StringIO()

...

print >> buf, "A = %d\n , B= %s\n" % (A, B)

...

print >> buf, "C=%d\n" % c

...

print >> f, buf.getvalue()

User · Answer

Take a look at  Literal String Interpolation  https   www python org dev peps pep-0498   I found it through the http   www malemburg com

User · Answer

Something like     greetings    Hello  name   format name    John    Hello John

User · Answer

To insert into a very long string it is nice to use names for the different arguments  instead of hoping they are in the right positions  This also makes it easier to replace multiple recurrences    gt  gt  gt   Coordinates   latitude    longitude   format latitude  37 24N   longitude  -115 81W    Coordinates  37 24N  -115 81W    Taken from Format examples  where all the other Format-related answers are also shown

User · Answer

Use the formatting operator     buf    quot A    d n   B   s n quot     a  b  print  gt  gt f  buf

User · Answer

You can use string formatting    gt  gt  gt  a 42  gt  gt  gt  b  bar   gt  gt  gt   The number is  d and the word is  s     a b   The number is 42 and the word is bar    But this is removed in Python 3  you should use  str format       gt  gt  gt  a 42  gt  gt  gt  b  bar   gt  gt  gt   The number is  0  and the word is  1   format a b   The number is 42 and the word is bar

User · Answer

If I understand your question correctly  format   is what you are looking for  along with its mini-language   Silly example for python 2 7 and up    gt  gt  gt  print         r n      format  Hello    world   Hello      world    For earlier python versions   tested with 2 6 2    gt  gt  gt  print   0      r n  1    format  Hello    world   Hello      world

User · Answer

Two approaches are to write to a string buffer or to write lines to a list and join them later   I think the StringIO approach is more pythonic  but didn t work before Python 2 6   from io import StringIO  with StringIO   as s     print  Hello   file s     print  Goodbye   file s       And later       with open  myfile    w   as f         f write s getvalue      You can also use these without a ContextMananger  s   StringIO      Currently  I m using a context manager class with a print function   This fragment might be useful to be able to insert debugging or odd paging requirements   class Report          usual init enter exit     def print self   args    kwargs           with StringIO   as s              print  args    kwargs  file s              out   s getvalue               stuff with out  with Report   as r     r print f This is  datetime date today        Yikes    end

User · Answer

Python has a   operator for this    gt  gt  gt  a   5  gt  gt  gt  b    hello   gt  gt  gt  buf    A    d n   B    s n     a  b   gt  gt  gt  print buf A   5    B   hello   gt  gt  gt  c   10  gt  gt  gt  buf    C    d n    c  gt  gt  gt  print buf C   10   See this reference for all supported format specifiers   You could as well use format    gt  gt  gt  print  This is the   th tome of     format 5   knowledge   This is the 5th tome of knowledge

User · Answer

I m not completely certain that I understand your goal  but you can use a StringIO instance as a buffer    gt  gt  gt  import StringIO   gt  gt  gt  buf   StringIO StringIO    gt  gt  gt  buf write  A    d  B    s n     3   bar     gt  gt  gt  buf write  C  d n    5   gt  gt  gt  print buf getvalue    A   3  B   bar C 5   Unlike sprintf  you just pass a string to buf write  formatting it with the   operator or the format method of strings    You could of course define a function to get the sprintf interface you re hoping for   def sprintf buf  fmt   args       buf write fmt   args    which would be used like this    gt  gt  gt  buf   StringIO StringIO    gt  gt  gt  sprintf buf   A    d  B    s n   3   foo    gt  gt  gt  sprintf buf   C    d n   5   gt  gt  gt  print buf getvalue    A   3  B   foo C   5

User · Answer

If you want something like the python3 print function but to a string   def sprint  args    kwargs       sio   io StringIO       print  args    kwargs  file sio      return sio getvalue      gt  gt  gt  x   sprint  abc   10    one    two      a   1   b   2    1  2  3    gt  gt  gt  x  abc 10   one    two     a   1   b   2   1  2  3  n    or without the   n  at the end   def sprint  args  end       kwargs       sio   io StringIO       print  args    kwargs  end end  file sio      return sio getvalue      gt  gt  gt  x   sprint  abc   10    one    two      a   1   b   2    1  2  3    gt  gt  gt  x  abc 10   one    two     a   1   b   2   1  2  3

[python] sprintf like functionality in Python

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