Beginning Python - From Novice to Professional
Beginning Python - From Novice to Professional Beginning Python - From Novice to Professional
CHAPTER 3 ■ WORKING WITH STRINGS 59 price_width = 10 item_width = width - price_width header_format = '%-*s%*s' format = '%-*s%*.2f' print '=' * width print header_format % (item_width, 'Item', price_width, 'Price') print '-' * width print format % (item_width, 'Apples', price_width, 0.4) print format % (item_width, 'Pears', price_width, 0.5) print format % (item_width, 'Cantaloupes', price_width, 1.92) print format % (item_width, 'Dried Apricots (16 oz.)', price_width, 8) print format % (item_width, 'Prunes (4 lbs.)', price_width, 12) print '=' * width The following is a sample run of the program: Please enter width: 35 =================================== Item Price —————————————————————————————— Apples 0.40 Pears 0.50 Cantaloupes 1.92 Dried Apricots (16 oz.) 8.00 Prunes (4 lbs.) 12.00 =================================== String Methods You have already encountered methods in lists. Strings have a much richer set of methods, in part because strings have “inherited” many of their methods from the string module where they resided as functions in earlier versions of Python (and where you may still find them, if you feel the need).
60 CHAPTER 3 ■ WORKING WITH STRINGS BUT STRING ISN’T DEAD Even though string methods have completely upstaged the string module, the module still includes a few constants and functions that aren’t available as string methods. The maketrans function is one example and will be discussed together with the translate method in the material that follows. Table 3-2 shows some useful constants available from string. For a more thorough description of the module, check out Section 4.1 of the Python Library Reference (http://python.org/doc/lib/module-string.html). Table 3-2. Useful Values from the string Module Constant Description string.digits A string containing the digits 0–9 string.letters A string containing all letters (upper- and lowercase) string.lowercase A string containing all lowercase letters string.printable A string containing all printable characters string.punctuation A string containing all punctuation characters string.uppercase A string containing all uppercase letters Because there are so many string methods, only some of the most useful ones are described here. For a full reference, see Appendix B. In the description of the string methods, you will find references to other, related string methods in this chapter (marked “See also”) or in Appendix B. find The find method finds a substring within a larger string. It returns the leftmost index where the substring is found. If it is not found, –1 is returned: >>> 'With a moo-moo here, and a moo-moo there'.find('moo') 7 >>> title = "Monty Python's Flying Circus" >>> title.find('Monty') 0 >>> title.find('Python') 6 >>> title.find('Flying') 15 >>> title.find('Zirquss') -1 In our first encounter with membership in Chapter 2, we created part of a spam filter by using the expression '$$$' in subject. We could also have used find (which would also have
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CHAPTER 3 ■ WORKING WITH STRINGS 59<br />
price_width = 10<br />
item_width = width - price_width<br />
header_format = '%-*s%*s'<br />
format = '%-*s%*.2f'<br />
print '=' * width<br />
print header_format % (item_width, 'Item', price_width, 'Price')<br />
print '-' * width<br />
print format % (item_width, 'Apples', price_width, 0.4)<br />
print format % (item_width, 'Pears', price_width, 0.5)<br />
print format % (item_width, 'Cantaloupes', price_width, 1.92)<br />
print format % (item_width, 'Dried Apricots (16 oz.)', price_width, 8)<br />
print format % (item_width, 'Prunes (4 lbs.)', price_width, 12)<br />
print '=' * width<br />
The following is a sample run of the program:<br />
Please enter width: 35<br />
===================================<br />
Item<br />
Price<br />
——————————————————————————————<br />
Apples 0.40<br />
Pears 0.50<br />
Cantaloupes 1.92<br />
Dried Apricots (16 oz.) 8.00<br />
Prunes (4 lbs.) 12.00<br />
===================================<br />
String Methods<br />
You have already encountered methods in lists. Strings have a much richer set of methods, in<br />
part because strings have “inherited” many of their methods from the string module where<br />
they resided as functions in earlier versions of <strong>Python</strong> (and where you may still find them, if<br />
you feel the need).
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