[Python-checkins] Cleanup and improve the regex tokenizer example. (GH-10426)

Fri Nov 9 04:19:39 EST 2018

https://github.com/python/cpython/commit/b83942c755a78f6d917743b73ed87a8fd9f367de
commit: b83942c755a78f6d917743b73ed87a8fd9f367de
branch: master
author: Raymond Hettinger <rhettinger at users.noreply.github.com>
committer: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
date: 2018年11月09日T01:19:33-08:00
summary:
Cleanup and improve the regex tokenizer example. (GH-10426)
1) Convert weird field name "typ" to the more standard "type".
2) For the NUMBER type, convert the value to an int() or float().
3) Simplify ``group(kind)`` to the shorter and faster ``group()`` call.
4) Simplify logic go a single if-elif chain to make this easier to extend.
5) Reorder the tests to match the order the tokens are specified.
 This isn't necessary for correctness but does make the example
 easier to follow.
6) Move the "column" calculation before the if-elif chain so that
 users have the option of using this value in error messages.
files:
M Doc/library/re.rst

diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index 31fb628dcaea..2f829559ff17 100644
--- a/Doc/library/re.rst
+++ b/Doc/library/re.rst
@@ -1609,38 +1609,40 @@ successive matches::
 import collections
 import re
 
- Token = collections.namedtuple('Token', ['typ', 'value', 'line', 'column'])
+ Token = collections.namedtuple('Token', ['type', 'value', 'line', 'column'])
 
 def tokenize(code):
 keywords = {'IF', 'THEN', 'ENDIF', 'FOR', 'NEXT', 'GOSUB', 'RETURN'}
 token_specification = [
- ('NUMBER', r'\d+(\.\d*)?'), # Integer or decimal number
- ('ASSIGN', r':='), # Assignment operator
- ('END', r';'), # Statement terminator
- ('ID', r'[A-Za-z]+'), # Identifiers
- ('OP', r'[+\-*/]'), # Arithmetic operators
- ('NEWLINE', r'\n'), # Line endings
- ('SKIP', r'[ \t]+'), # Skip over spaces and tabs
- ('MISMATCH',r'.'), # Any other character
+ ('NUMBER', r'\d+(\.\d*)?'), # Integer or decimal number
+ ('ASSIGN', r':='), # Assignment operator
+ ('END', r';'), # Statement terminator
+ ('ID', r'[A-Za-z]+'), # Identifiers
+ ('OP', r'[+\-*/]'), # Arithmetic operators
+ ('NEWLINE', r'\n'), # Line endings
+ ('SKIP', r'[ \t]+'), # Skip over spaces and tabs
+ ('MISMATCH', r'.'), # Any other character
 ]
 tok_regex = '|'.join('(?P<%s>%s)' % pair for pair in token_specification)
 line_num = 1
 line_start = 0
 for mo in re.finditer(tok_regex, code):
 kind = mo.lastgroup
- value = mo.group(kind)
- if kind == 'NEWLINE':
+ value = mo.group()
+ column = mo.start() - line_start
+ if kind == 'NUMBER':
+ value = float(value) if '.' in value else int(value)
+ elif kind == 'ID' and value in keywords:
+ kind = value
+ elif kind == 'NEWLINE':
 line_start = mo.end()
 line_num += 1
+ continue
 elif kind == 'SKIP':
- pass
+ continue
 elif kind == 'MISMATCH':
 raise RuntimeError(f'{value!r} unexpected on line {line_num}')
- else:
- if kind == 'ID' and value in keywords:
- kind = value
- column = mo.start() - line_start
- yield Token(kind, value, line_num, column)
+ yield Token(kind, value, line_num, column)
 
 statements = '''
 IF quantity THEN
@@ -1654,25 +1656,25 @@ successive matches::
 
 The tokenizer produces the following output::
 
- Token(typ='IF', value='IF', line=2, column=4)
- Token(typ='ID', value='quantity', line=2, column=7)
- Token(typ='THEN', value='THEN', line=2, column=16)
- Token(typ='ID', value='total', line=3, column=8)
- Token(typ='ASSIGN', value=':=', line=3, column=14)
- Token(typ='ID', value='total', line=3, column=17)
- Token(typ='OP', value='+', line=3, column=23)
- Token(typ='ID', value='price', line=3, column=25)
- Token(typ='OP', value='*', line=3, column=31)
- Token(typ='ID', value='quantity', line=3, column=33)
- Token(typ='END', value=';', line=3, column=41)
- Token(typ='ID', value='tax', line=4, column=8)
- Token(typ='ASSIGN', value=':=', line=4, column=12)
- Token(typ='ID', value='price', line=4, column=15)
- Token(typ='OP', value='*', line=4, column=21)
- Token(typ='NUMBER', value='0.05', line=4, column=23)
- Token(typ='END', value=';', line=4, column=27)
- Token(typ='ENDIF', value='ENDIF', line=5, column=4)
- Token(typ='END', value=';', line=5, column=9)
+ Token(type='IF', value='IF', line=2, column=4)
+ Token(type='ID', value='quantity', line=2, column=7)
+ Token(type='THEN', value='THEN', line=2, column=16)
+ Token(type='ID', value='total', line=3, column=8)
+ Token(type='ASSIGN', value=':=', line=3, column=14)
+ Token(type='ID', value='total', line=3, column=17)
+ Token(type='OP', value='+', line=3, column=23)
+ Token(type='ID', value='price', line=3, column=25)
+ Token(type='OP', value='*', line=3, column=31)
+ Token(type='ID', value='quantity', line=3, column=33)
+ Token(type='END', value=';', line=3, column=41)
+ Token(type='ID', value='tax', line=4, column=8)
+ Token(type='ASSIGN', value=':=', line=4, column=12)
+ Token(type='ID', value='price', line=4, column=15)
+ Token(type='OP', value='*', line=4, column=21)
+ Token(type='NUMBER', value=0.05, line=4, column=23)
+ Token(type='END', value=';', line=4, column=27)
+ Token(type='ENDIF', value='ENDIF', line=5, column=4)
+ Token(type='END', value=';', line=5, column=9)
 
 
 .. [Frie09] Friedl, Jeffrey. Mastering Regular Expressions. 3rd ed., O'Reilly
