what does % stand for in an expression ?

[arbiel]

Hi
I found the following example in the python doc :

from typing import NamedTuple
import re

class Token(NamedTuple):
    type: str
    value: str
    line: int
    column: int

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
    ]
    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()
        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':
            continue
        elif kind == 'MISMATCH':
            raise RuntimeError(f'{value!r} unexpected on line {line_num}')
        yield Token(kind, value, line_num, column)

statements = '''
    IF quantity THEN
        total := total + price * quantity;
        tax := price * 0.05;
    ENDIF;
'''

for token in tokenize(statements):
    print(token)

Line 22 reads

 tok_regex = '|'.join('(?P<%s>%s)' % pair for pair in token_specification)

I suppose that each %s stands for the corresponding element of pair and that % stands for the tuple itself.

Where can I find any explanation of this coding ?

Thank you for having read my post.

Arbiel

[buran]

Check the docs: Old-style string formatting

Also https://docs.python.org/3/library/stdtyp...formatting

Note, there are newer/better/powerful string formatting methods

[arbiel]

Check the docs: Old-style string formatting

Also https://docs.python.org/3/library/stdtyp...formatting

Note, there are newer/better/powerful string formatting methods

OK

Understood.

Thanks

Arbiel

[carlbidwell]

In Python, the % operator is the modulo operator, it returns the remainder when the left operand is divided by the right operand. For more: Python Forum

[Gribouillis]

Generally speaking

x % y

is equivalent to

x.__mod__(y)

if the type of x implements a __mod__() method. Otherwise it is equivalent to

y.__rmod__(x)

if the type of y implements a __rmod__() method. Otherwise it raises a TypeError.

The effect and result depends on what these methods do, which can be arbitrary.