Python — Why 1.__str__() is invalid syntax

CPython tokenize workflow:

1. https://github.com/python/cpython/blob/master/Lib/tokenize.py#L535
2. NUMBER — https://github.com/python/cpython/blob/master/Lib/tokenize.py#L80
3. Imagnumber — https://github.com/python/cpython/blob/master/Lib/tokenize.py#L79
4. Floatnumber — https://github.com/python/cpython/blob/master/Lib/tokenize.py#L78
5. Intnumber — https://github.com/python/cpython/blob/master/Lib/tokenize.py#L73

We can manually parse the statement to tokens and see how cpython works here

$ echo "1.__str__()" | python3 tokenize.py
1,0-1,2:            NUMBER         '1.'
1,2-1,9:            NAME           '__str__'
1,9-1,10:           OP             '('
1,10-1,11:          OP             ')'
1,11-1,12:          NEWLINE        '\n'
2,0-2,0:            ENDMARKER      ''

we can see here, it takes ‘1.’ to a number, and means Floatnumber is in a higher priority than Intnumber.

So we have two ways to make it work:

>>> (1).__str__()
'1'
$ echo "(1).__str__()" | python3 tokenize.py
1,0-1,1:            OP             '('
1,1-1,2:            NUMBER         '1'
1,2-1,3:            OP             ')'
1,3-1,4:            OP             '.'
1,4-1,11:           NAME           '__str__'
1,11-1,12:          OP             '('
1,12-1,13:          OP             ')'
1,13-1,14:          NEWLINE        '\n'
2,0-2,0:            ENDMARKER      ''
>>> 1..__str__()
'1.0'
$ echo "1..__str__()" | python3 tokenize.py
1,0-1,2:            NUMBER         '1.'
1,2-1,3:            OP             '.'
1,3-1,10:           NAME           '__str__'
1,10-1,11:          OP             '('
1,11-1,12:          OP             ')'
1,12-1,13:          NEWLINE        '\n'
2,0-2,0:            ENDMARKER      ''

But looks like the second one is not the expected one.

Anyway, that’s all.