[Python-checkins] Cleanup and improve the regex tokenizer example. (GH-10426) (#10427)

[Raymond Hettinger]

https://github.com/python/cpython/commit/33fd60d4c3fd95ef1c8edf83bd4a3c203edc1cad
commit: 33fd60d4c3fd95ef1c8edf83bd4a3c203edc1cad
branch: 3.7
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: Raymond Hettinger <rhettinger at users.noreply.github.com>
date: 2018-11-09T01:26:55-08:00
summary:

Cleanup and improve the regex tokenizer example. (GH-10426) (#10427)

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.
(cherry picked from commit b83942c755a78f6d917743b73ed87a8fd9f367de)

Co-authored-by: Raymond Hettinger <rhettinger at users.noreply.github.com>

files:
M Doc/library/re.rst

diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index 6cd7ebc89734..e6455bb359df 100644
--- a/Doc/library/re.rst
+++ b/Doc/library/re.rst
@@ -1607,38 +1607,40 @@ 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
@@ -1652,25 +1654,25 @@ 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