Python printf

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

Python printf

To format data into a string in python, use the % operator as python doesn't have an sprintf or printf function. So why have I entitled today's entry "python printf? Because this in one of the most frequently asked, and infrequently answered questions.

The % operator with a string to its left formats the value to the right using the (sprintf style) string to to the left of the operator. Where you want to format more that one value, use a tuple to the right.

Here's an example in which I've formatted an integer to return a three digit number padded with leading zeros:

>>> licensed = 7         

>>> callin = "Agent %03d" % licensed

>>> print callin

Agent 007

>>>

We've got an example using a tuple in our course material and there's an example using a format string variable and aligning output columns in python there too. There is further documentation of pythons' % operator on the Python documentation site (well hidden, so I give you the link!)

Aside - why no printf in python? Because you don't need it and the alternative is neater and better. Arguably, there shouldn't be a printf function in any other language either, as it both formats the values AND sends them to the output channel - doing two logical operations in a single call, and you're bound to want to separate them at some stage. Instead, there should be two functions. There usually are ... and from a purist's viewpoint, sprintf followed by echo or print is much more maintainable that a single sprintf.

Illustration - delegates on a Python Programming training course at Well House Manor - our residential training centre.
(written 2005-11-15, updated 2010-06-19)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

Y108 - Python - String Handling
  [324] The backtick operator in Python and Perl - (2005-05-25)
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  [560] The fencepost problem - (2006-01-10)
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  [954] Splitting Pythons in Bradford - (2006-11-29)
  [970] String duplication - x in Perl, * in Python and Ruby - (2006-12-07)
  [1110] Python - two different splits - (2007-03-15)
  [1195] Regular Express Primer - (2007-05-20)
  [1517] Python - formatting objects - (2008-01-24)
  [1608] Underlining in Perl and Python - the x and * operator in use - (2008-04-12)
  [1876] Python Regular Expressions - (2008-11-08)
  [2284] Strings as collections in Python - (2009-07-12)
  [2406] Pound Sign in Python Program - (2009-09-15)
  [2692] Flexible search and replace in Python - (2010-03-25)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2780] Formatted Printing in Python - (2010-05-25)
  [2814] Python - splitting and joining strings - (2010-06-16)
  [3090] Matching to a string - what if it matches in many possible ways? - (2010-12-17)
  [3218] Matching a license plate or product code - Regular Expressions - (2011-03-28)
  [3349] Formatting output in Python through str.format - (2011-07-07)
  [3468] Python string formatting - the move from % to str.format - (2011-10-08)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
  [3886] Formatting output - why we need to, and first Python example - (2012-10-09)
  [4027] Collections in Python - list tuple dict and string. - (2013-03-04)
  [4152] Why are bus fares so high? - (2013-08-18)
  [4213] Formatting options in Python - (2013-11-16)
  [4307] Identifying and clearing denial of service attacks on your Apache server - (2014-09-27)
  [4360] Python - comparison of old and new string formatters - (2014-12-22)
  [4593] Command line parameter handling in Python via the argparse module - (2015-12-08)
  [4595] Python formatting update - including named completions - (2015-12-10)
  [4659] Prining a pound sign from Python AND running from the command line at the same time - (2016-03-03)

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