Why is "1.real" a syntax error but "1 .real" valid in Python?

Question

So I saw these two questions on twitter. How is 1.real a syntax error but 1 .real is not?

>>> 1.real   File "<stdin>", line 1     1.real          ^ SyntaxError: invalid syntax >>> 1 .real 1 >>> 1. real   File "<stdin>", line 1     1. real           ^ SyntaxError: invalid syntax >>> 1 . real 1 >>> 1..real 1.0 >>> 1 ..real   File "<stdin>", line 1     1 ..real        ^ SyntaxError: invalid syntax >>> 1.. real 1.0 >>> 1 .. real   File "<stdin>", line 1     1 .. real        ^ SyntaxError: invalid syntax 

Answer 1

I guess that the . is greedily parsed as part of a number, if possible, making it the float 1., instead of being part of the method call.

Spaces are not allowed around the decimal point, but you can have spaces before and after the . in a method call. If the number is followed by a space, the parse of the number is terminated, so it's unambiguous.

Let's look at the different cases and how they are parsed:

>>> 1.real    # parsed as (1.)real  -> missing '.' >>> 1 .real   # parsed as (1).real  -> okay >>> 1. real   # parsed as (1.)real  -> missing '.' >>> 1 . real  # parsed as (1).real  -> okay >>> 1..real   # parsed as (1.).real -> okay >>> 1 ..real  # parsed as (1)..real -> one '.' too much >>> 1.. real  # parsed as (1.).real -> okay >>> 1 .. real # parsed as (1)..real -> one '.' too much