The difference between sys.stdout.write and print?

Question

Are there situations in which sys.stdout.write() is preferable to print?

(Examples: better performance; code that makes more sense)

Solution 1

print is just a thin wrapper that formats the inputs (modifiable, but by default with a space between args and newline at the end) and calls the write function of a given object. By default this object is sys.stdout, but you can pass a file using the "chevron" form. For example:

print >> open('file.txt', 'w'), 'Hello', 'World', 2+3

See: https://docs.python.org/2/reference/simple_stmts.html?highlight=print#the-print-statement

---

In Python 3.x, print becomes a function, but it is still possible to pass something other than sys.stdout thanks to the fileargument.

print('Hello', 'World', 2+3, file=open('file.txt', 'w'))

See https://docs.python.org/3/library/functions.html#print

---

In Python 2.6+, print is still a statement, but it can be used as a function with

from __future__ import print_function

---

Update: Bakuriu commented to point out that there is a small difference between the print function and the print statement (and more generally between a function and a statement).

In case of an error when evaluating arguments:

print "something", 1/0, "other" #prints only something because 1/0 raise an Exception

print("something", 1/0, "other") #doesn't print anything. The function is not called

Solution 2

print first converts the object to a string (if it is not already a string). It will also put a space before the object if it is not the start of a line and a newline character at the end.

When using stdout, you need to convert the object to a string yourself (by calling "str", for example) and there is no newline character.

So

print 99

is equivalent to:

import sys
sys.stdout.write(str(99) + '\n')

Solution 3

Here's some sample code based on the book Learning Python by Mark Lutz that addresses your question:

import sys
temp = sys.stdout                 # store original stdout object for later
sys.stdout = open('log.txt', 'w') # redirect all prints to this log file
print("testing123")               # nothing appears at interactive prompt
print("another line")             # again nothing appears. it's written to log file instead
sys.stdout.close()                # ordinary file object
sys.stdout = temp                 # restore print commands to interactive prompt
print("back to normal")           # this shows up in the interactive prompt

Opening log.txt in a text editor will reveal the following:

testing123
another line

Solution 4

My question is whether or not there are situations in which sys.stdout.write() is preferable to print

After finishing developing a script the other day, I uploaded it to a unix server. All my debug messages used print statements, and these do not appear on a server log.

This is a case where you may need sys.stdout.write instead.

Solution 5

There's at least one situation in which you want sys.stdout instead of print.

When you want to overwrite a line without going to the next line, for instance while drawing a progress bar or a status message, you need to loop over something like

Note carriage return-> "\rMy Status Message: %s" % progress

And since print adds a newline, you are better off using sys.stdout.

View more solutions