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.

diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index 31fb628dcaeaf31ec467deb93167b8d0d61cc7fc..2f829559ff174a1186bb33ef846f87ab1c58131f 100644 (file)
--- 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