From 6c585aeb604350d2aa98ed0f0a3c5590e64f068d Mon Sep 17 00:00:00 2001 From: Mark Pilgrim Date: Thu, 16 Jul 2009 12:30:25 -0400 Subject: [PATCH] move some explanatory stuff to the files chapter --- generators.html | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/generators.html b/generators.html index 9e5bb5f..afcff1e 100755 --- a/generators.html +++ b/generators.html @@ -274,15 +274,15 @@ $ $ s return [matches_rule, apply_rule] rules = [] -with open('plural4-rules.txt') as pattern_file: ② - for line in pattern_file: ③ - pattern, search, replace = line.split(None, 3) ④ - rules.append(build_match_and_apply_functions( ⑤ +with open('plural4-rules.txt', encoding='utf-8') as pattern_file: ② + for line in pattern_file: ③ + pattern, search, replace = line.split(None, 3) ④ + rules.append(build_match_and_apply_functions( ⑤ pattern, search, replace))
  1. The build_match_and_apply_functions() function has not changed. You’re still using closures to build two functions dynamically that use variables defined in the outer function. -
  2. The global open() function opens a file and returns a file object. In this case, the file we’re opening contains the pattern strings for pluralizing nouns. The with statement creates what’s called a context: when the with block ends, Python will automatically close the file, even if an exception is raised inside the with block. You’ll learn more about with blocks in the Files chapter. -
  3. The for line in <fileobject> idiom reads data from the open file, one line at a time, and assigns the text to the line variable. A “line” of a text file is just what you think it is — a sequence of characters delimited by a carriage return. Of course, it can’t really be that simple, can it? Text files can use several different characters to mark the end of a line. Some use a carriage return character, others use a line feed character, and some use both characters at the end of every line. Python handles all of these cases automatically, so you can say, “Hey, I want to read this text file one line at a time” and it will Just Work. You’ll learn more about reading from and writing to in the Files chapter. +
  4. The global open() function opens a file and returns a file object. In this case, the file we’re opening contains the pattern strings for pluralizing nouns. The with statement creates what’s called a context: when the with block ends, Python will automatically close the file, even if an exception is raised inside the with block. You’ll learn more about with blocks and file objects in the Files chapter. +
  5. The for line in <fileobject> idiom reads data from the open file, one line at a time, and assigns the text to the line variable. You’ll learn more about reading from and writing to in the Files chapter.
  6. Each line in the file really has three values, but they’re separated by whitespace (tabs or spaces, it makes no difference). To split it out, use the split() string method. The first argument to the split() method is None, which means “split on any whitespace (tabs or spaces, it makes no difference).” The second argument is 3, which means “split on whitespace 3 times, then discard the rest of the line.” A line like [sxz]$ $ es will be broken up into the list ['[sxz]$', '$', 'es'], which means that pattern will get '[sxz]$', search will get '$', and replace will get 'es'. That’s a lot of power in one little line of code.