Starting with Python 2.6 there is a new format function to do string formatting. I’ve always been a bit overwhelmed by the official Format String Syntax documentation so I’ll try to present it to you with more examples.
Python so far had the ‘%’ operator. It’s been deprecated with Python 2.6 and removed from Python 3. Instead string has a new format method.
>>> "This is an %s-style formatting" % "old"
'This is an old-style formatting'
>>> "This is a {0}-style formatting".format("new")
'This is an new-style formatting'
Formatting options go after a colon, for example the width specifications together with alignment options which are mostly useful for tabular representations. Let’s print the following table as an exercise:
| * Company * | * Employees * |
| Apple | 35000 |
| Nektoon | 000000000000005 |
| local.ch | 24.80 |
Note the centered headlines, and the different left- and right-align values with some padding and floating point formatting dropped in for good measure.
This is easily achieved with the following code:
>>> "| {0:^15} | {1:^15} |".format("* Company *", "* Employees *")
>>> "| {0:15} | {1:<15} |".format("Apple", 35000)
>>> "| {0:>15} | {1:015} |".format("Nektoon", 5)
>>> "| {0:15} | {1:15.2f} |".format("local.ch", 24.8)
As you can see, numbers are right-aligned and strings left-aligned by default. But you can force a different behaviour by manually aligning them using ‘<’ or ‘>’.
Last but not least, format also accepts named parameters:
>>> "| {company:15} | {employees:15} |".format(
... company="Nektoon", employees=5)
'| Nektoon | 5 |'
That covers the most basic use cases of the format method. Having read this introduction, you can now use the Format String Syntax documentation as the reference it is.
The Python interpreter session is also available as a syntax-colored paste on Lodge It.
This post is part of the Python on the toilet series.