Python string formatting vs format

0 votes

Python 2.6 introduced the str.format() method with a slightly different syntax from the existing %operator. Which is better and for what situations?

  1. The following uses each method and has the same outcome, so what is the difference?

  2. #!/usr/bin/python
    sub1 = "python string!"
    sub2 =
    "an arg"
    a =
    "i am a %s" % sub1
    b =
    "i am a {0}".format(sub1)
    c =
    "with %(kwarg)s!" % {'kwarg':sub2}
    d =
    "with {kwarg}!".format(kwarg=sub2)
    print a # "i am a python string!"
    print b # "i am a python string!"
    print c # "with an arg!"
    print d # "with an arg!"

  3. Furthermore when does string formatting occur in Python? For example, if my logging level is set to HIGH will I still take a hit for performing the following % operation? And if so, is there a way to avoid this?

log.debug("some debug info: %s" % some_info)

Aug 17, 2018 in Python by bug_seeker
• 15,530 points

1 answer to this question.

0 votes

To answer your first question... .format just seems more sophisticated in many ways. An annoying thing about % is also how it can either take a variable or a tuple. You'd think the following would always work:

"hi there %s" % name

yet, if name happens to be (1, 2, 3), it will throw a TypeError. To guarantee that it always prints, you'd need to do

"hi there %s" % (name,) # supply the single argument as a single-item tuple

which is just ugly. .format doesn't have those issues. Also in the second example you gave, the .format example is much cleaner looking.

Why would you not use it?

  • not knowing about it (me before reading this)

  • having to be compatible with Python 2.5

To answer your second question, string formatting happens at the same time as any other operation - when the string formatting expression is evaluated. And Python, not being a lazy language, evaluates expressions before calling functions, so in your log.debug example, the expression "some debug info: %s"%some_infowill first evaluate to, e.g. "some debug info: roflcopters are active", then that string will be passed to log.debug()

answered Aug 17, 2018 by Priyaj
• 58,100 points

Related Questions In Python

0 votes
2 answers

What's the difference between %s and %d in Python string formatting?

The reason is that they are using ...READ MORE

answered Feb 8, 2022 in Python by Rahul
• 9,670 points
0 votes
0 answers

TypeError: not all arguments converted during string formatting python

The program is supposed to take in ...READ MORE

Dec 22, 2022 in Python by erzan
• 640 points
0 votes
2 answers
+1 vote
2 answers

how can i count the items in a list?

Syntax :            list. count(value) Code: colors = ['red', 'green', ...READ MORE

answered Jul 7, 2019 in Python by Neha
• 330 points

edited Jul 8, 2019 by Kalgi 3,471 views
0 votes
1 answer
+5 votes
6 answers

Lowercase in Python

You can simply the built-in function in ...READ MORE

answered Apr 11, 2018 in Python by hemant
• 5,790 points
+1 vote
2 answers

Python string formatting: % vs. .format

Using Python format() function is what the ...READ MORE

answered Apr 11, 2019 in Python by Dasa Ravi
+7 votes
8 answers

Difference for string comparison in Python: 'is' vs. ==

If we use "==" means both variables ...READ MORE

answered Sep 3, 2018 in Python by Parul Raheja
webinar_success Thank you for registering Join Edureka Meetup community for 100+ Free Webinars each month JOIN MEETUP GROUP