Core Python Programming (2nd Edition)

method (see example below). There is really no longer a need to import the string module unless you
are trying to access some of the older string constants which that module defines.
Note: Although easier to learn for beginners, we recommend not using string concatenation when
performance counts. The reason is that for every string that is part of a concatenation, Python has to
allocate new memory for all strings involved, including the result. Instead, we recommend you either
use the string format operator ( % ), as in the examples below, or put all of the substrings in a list, and
using one join() call to put them all together:
>>> '%s %s' % ('Spanish', 'Inquisition')
'Spanish Inquisition'
>>>
>>> s = ' '.join(('Spanish', 'Inquisition', 'Made Easy'))
>>> s
'Spanish Inquisition Made Easy'
>>>
>>> # no need to import string to use string.upper():
>>> ('%s%s' % (s[:3], s[20])).upper()
'SPAM'
Compile-Time String Concatenation
The above syntax using the addition operator performs the string concatenation at runtime, and its use
is the norm. There is a less frequently used syntax that is more of a programmer convenience feature.
Python's syntax allows you to create a single string from multiple string literals placed adjacent to each
other in the body of your source code:
>>> foo = "Hello" 'world!'
>>> foo
'Helloworld!'
It is a convenient way to split up long strings without unnecessary backslash escapes. As you can see
from the above, you can mix quotation types on the same line. Another good thing about this feature is
that you can add comments too, like this example:
>>> f = urllib.urlopen('http://' # protocol
... 'localhost' # hostname
... ':8000' # port
... '/cgi-bin/friends2.py') # file
As you can imagine, here is what urlopen() really gets as input:
>>> 'http://' 'localhost' ':8000' '/cgi-bin/friends2.py'
'http://localhost:8000/cgi-bin/friends2.py'
Regular String Coercion to Unicode
When concatenating regular and Unicode strings, regular strings are converted to Unicode first before
the operation occurs: