UW AMath High Performance Scientific Computing
AMath 483/583 Class Notes
Spring Quarter, 2013

Table Of Contents

Previous topic

Python functions

Next topic

Numerics in Python

This Page

Python strings

See this List of methods applicable to strings

String formatting

Often you want to construct a string that incorporates the values of some variables. This can be done using the form format % values where format is a string that describes the desired format and values is a single value or tuple of values that go into various slots in the format.

See String Formatting Operations

This is best learned from some examples:

>>> x = 45.6
>>> s = "The value of x is %s"  % x
>>> s
'The value of x is 45.6'

The %s in the format string means to convert x to a string and insert into the format. It will use as few spaces as possible.

>>> s = "The value of x is %21.14e"  % x
>>> s
'The value of x is  4.56000000000000e+01'

In the case above, exponential notation is used with 14 digits to the right of the decimal point, put into a field of 21 digits total. (You need at least 7 extra characters to leave room for a possible minus sign as well as the first digit, the decimal point, and the exponent such as e+01.

>>> y = -0.324876
>>> s = "Now x is %8.3f and y is %8.3f" % (x,y)
>>> s
'Now x is   45.600 and y is   -0.325'

In this example, fixed notation is used instead of scientific notation, with 3 digits to the right of the decimal point, in a field 8 characters wide. Note that y has been rounded.

In the last example, two variables are inserted into the format string.