Beginning Python - From Novice to Professional
Beginning Python - From Novice to Professional Beginning Python - From Novice to Professional
CHAPTER 1 ■ INSTANT HACKING: THE BASICS 27 Long Strings If you want to write a really long string, one that spans several lines, you can use triple quotes instead of ordinary quotes: print '''This is a very long string. It continues here. And it's not over yet. "Hello, world!" Still here.''' You can also use triple double quotes, """like this""". Note that because of the distinctive enclosing quotes, both single and double quotes are allowed inside, without being backslashescaped. ■Tip Ordinary strings can also span several lines. If the last character on a line is a backslash, the line break itself is “escaped,” and is ignored. For example: print "Hello, \ world!" would print out Hello, world!. The same goes for expressions and statements in general: >>> 1 + 2 + \ 4 + 5 12 >>> print \ 'Hello, world' Hello, world Raw Strings Raw strings aren’t too picky about backslashes, which can be very useful sometimes. 10 In ordinary strings, the backslash has a special role: It escapes things, letting you put things into your string that you couldn’t normally write directly. For example, a new line is written \n, and can be put into a string like this: >>> print 'Hello,\nworld!' Hello, world! This is normally just dandy, but in some cases it’s not what you want. What if you wanted the string to include a backslash followed by an n? You might want to put the DOS pathname C:\nowhere into a string, for example: 10. Especially when writing regular expressions. More about those in Chapter 10.
28 CHAPTER 1 ■ INSTANT HACKING: THE BASICS >>> path = 'C:\nowhere' >>> path 'C:\nowhere' This looks correct, until you print it and discover the flaw: >>> print path C: owhere Not exactly what we were after, is it? So what do we do? We can escape the backslash itself: >>> print 'C:\\nowhere' C:\nowhere This is just fine. But for long paths, you wind up with a lot of backslashes: path = 'C:\\Program Files\\fnord\\foo\\bar\\baz\\frozz\\bozz' Raw strings are useful in such cases. They don’t treat the backslash as a special character at all. Every character you put into a raw string stays the way you wrote it: >>> print r'C:\nowhere' C:\nowhere >>> print r'C:\Program Files\fnord\foo\bar\baz\frozz\bozz' C:\Program Files\fnord\foo\bar\baz\frozz\bozz As you can see, raw strings are written with an r in front. It would seem that you can put almost anything inside a raw string, and that is almost true. Of course, quotes have to be escaped as usual, although that means that you get a backslash in your final string, too: >>> print r'Let\'s go!' Let\'s go! The one thing you can’t have in a raw string is a final backslash. In other words, the last character in a raw string cannot be a backslash. Given the previous example, that ought to be obvious. If the last character (before the final quote) is a backslash, Python won’t know whether to end the string or not: >>> print r"This is illegal\" SyntaxError: invalid token Okay, so it’s reasonable, but what if you want the last character in your raw string to be a backslash? (Perhaps it’s the end of a DOS path, for example.) Well, I’ve given you a whole bag of tricks in this section that should help you solve that problem, but basically you need to put the backslash in a separate string. A simple way of doing that is the following: >>> print r'C:\Program Files\foo\bar' '\\' C:\Program Files\foo\bar\ Note that you can use both single and double quotes with raw strings. Even triple-quoted strings can be raw.
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CHAPTER 1 ■ INSTANT HACKING: THE BASICS 27<br />
Long Strings<br />
If you want <strong>to</strong> write a really long string, one that spans several lines, you can use triple quotes<br />
instead of ordinary quotes:<br />
print '''This is a very long string.<br />
It continues here.<br />
And it's not over yet.<br />
"Hello, world!"<br />
Still here.'''<br />
You can also use triple double quotes, """like this""". Note that because of the distinctive<br />
enclosing quotes, both single and double quotes are allowed inside, without being backslashescaped.<br />
■Tip Ordinary strings can also span several lines. If the last character on a line is a backslash, the line break<br />
itself is “escaped,” and is ignored. For example:<br />
print "Hello, \<br />
world!"<br />
would print out Hello, world!. The same goes for expressions and statements in general:<br />
>>> 1 + 2 + \<br />
4 + 5<br />
12<br />
>>> print \<br />
'Hello, world'<br />
Hello, world<br />
Raw Strings<br />
Raw strings aren’t <strong>to</strong>o picky about backslashes, which can be very useful sometimes. 10 In ordinary<br />
strings, the backslash has a special role: It escapes things, letting you put things in<strong>to</strong> your<br />
string that you couldn’t normally write directly. For example, a new line is written \n, and can<br />
be put in<strong>to</strong> a string like this:<br />
>>> print 'Hello,\nworld!'<br />
Hello,<br />
world!<br />
This is normally just dandy, but in some cases it’s not what you want. What if you wanted the<br />
string <strong>to</strong> include a backslash followed by an n? You might want <strong>to</strong> put the DOS pathname<br />
C:\nowhere in<strong>to</strong> a string, for example:<br />
10. Especially when writing regular expressions. More about those in Chapter 10.
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