Python Tutorial (2.7.1) by Python Software Foundation

Author:Python Software Foundation
Language: eng
Format: mobi
Tags: CS, Programming, IT
Publisher: Python Software Foundation
Published: 2011-01-18T23:00:00+00:00

Here are two ways to write a table of squares and cubes:

>>> for x in range(1, 11):

... print repr(x).rjust(2), repr(x*x).rjust(3),

... # Note trailing comma on previous line

... print repr(x*x*x).rjust(4)

...

1 1 1

2 4 8

3 9 27

4 16 64

5 25 125

6 36 216

7 49 343

8 64 512

9 81 729

10 100 1000

>>> for x in range(1,11):

... print '{0:2d} {1:3d} {2:4d}'.format(x, x*x, x*x*x)

...

1 1 1

2 4 8

3 9 27

4 16 64

5 25 125

6 36 216

7 49 343

8 64 512

9 81 729

10 100 1000

(Note that in the first example, one space between each column was added by the way print works: it always adds spaces between its arguments.)

This example demonstrates the rjust() method of string objects, which right-justifies a string in a field of a given width by padding it with spaces on the left. There are similar methods ljust() and center(). These methods do not write anything, they just return a new string. If the input string is too long, they don't truncate it, but return it unchanged; this will mess up your column lay-out but that's usually better than the alternative, which would be lying about a value. (If you really want truncation you can always add a slice operation, as in x.ljust(n)[:n].)

There is another method, zfill(), which pads a numeric string on the left with zeros. It understands about plus and minus signs:

>>> '12'.zfill(5)

'00012'

>>> '-3.14'.zfill(7)

'-003.14'

>>> '3.14159265359'.zfill(5)

'3.14159265359'

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