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 Pyt

Answer 1

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:

>>> print "{} ...\r\n {}!".format("Hello", "world")
Hello ...
 world!

For earlier python versions: (tested with 2.6.2)

>>> print "{0} ...\r\n {1}!".format("Hello", "world")
Hello ...
 world!

Answer 2

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()

Answer 3

Take a look at "Literal String Interpolation" https://www.python.org/dev/peps/pep-0498/

I found it through the http://www.malemburg.com/

Answer 4

Python has a % operator for this.

>>> a = 5
>>> b = "hello"
>>> buf = "A = %d\n , B = %s\n" % (a, b)
>>> print buf
A = 5
 , B = hello

>>> c = 10
>>> buf = "C = %d\n" % c
>>> print buf
C = 10

See this reference for all supported format specifiers.

You could as well use format:

>>> print "This is the {}th tome of {}".format(5, "knowledge")
This is the 5th tome of knowledge

Answer 5

Something like...

greetings = 'Hello {name}'.format(name = 'John')

Hello John

Answer 6

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=':')