Question

I would like to write a function in Python that will take arguments just like print does but instead of printing the strings to stdout, I would like to write the strings formatted into a text file.

How do I define the arguments for such a function arguments to accept the string formatting, I’m wondering?

I am looking for something that would replace

print "Test"

with

MyLog "Test"

but the % rguments should also be supported.
So far I have only come up with this:

def logger(txt):    
fh = open (LOGFILE, "a") #Get handle in append mode
fh.write(txt)
fh.close()
print txt
return True 

which works fine for a simple string but i don’t think it’ll take the % arguments nor will I be able to call it like logger “TEST”

Answer 1

You can use the “print chevron” statement to do what you want like this:

with open('filename.txt', 'w') as f:
  print >> f, my_object

See the documentation for the print statement.

Of course, it probably is better practice to use the print() function as Martijn Pieters suggests.

Update

If I change your logger function to use the print chevron syntax, I get this:

def logger(txt):    
  fh = open (LOGFILE, "a") #Get handle in append mode
  fh.write(txt)
  fh.close()
  print >>fh, txt
  return True 

If you call this function like:

now, duration = 4.0, 2.0
logger("User request at %f time took %f seconds." % (now, duration))

You’ll have a line in your log file that looks like this:

User request at 4.0 time took 2.0 seconds.

So you can use this with the % formatting (although you really should take a look at the new-style formatting), but you won’t be able to call it like:

logger "User request at %f time took %f seconds." % (now, duration)

That’s because print is a simple statement, which is a language level construct, and you can’t add those to Python.