When an equal sign is used instead of a colon in creating a dict literal, depending on the context, either the "bad token" is misidentified OR the would-be helpful error message is incorrect in this particular case.

1) Example of bad token.
Previously, the = sign was identified correctly:

>>> ages = {'Alice'=22, 'Bob'=23}
  File "<stdin>", line 1
    ages = {'Alice'=22, 'Bob'=23}
                   ^
SyntaxError: invalid syntax

With Python 3.10.0b1, the comma is identified as the bad token:

>>> ages = {'Alice'=22, 'Bob'=23}
  File "<stdin>", line 1
    ages = {'Alice'=22, 'Bob'=23}
                      ^
SyntaxError: invalid syntax


2) Example of incorrect error message

Previously, we got the traditional and unhelpful "invalid syntax" but with the bad token identified correctly:

>>> ages = {'Alice'=22}
  File "<stdin>", line 1
    ages = {'Alice'=22}
                   ^
SyntaxError: invalid syntax

With Python 3.10.0b1, we get the following:

>>> ages = {'Alice'=22}
  File "<stdin>", line 1
    ages = {'Alice'=22}
            ^^^^^^^
SyntaxError: cannot assign to literal here. Maybe you meant '==' instead of '='?

I suspect that the ratio (== suggestion correct/ : suggestion correct) would be vanishingly small. ;-)

The bad token example needs a fix but the second is actually ok because we have another type we write within curly braces "{" and there the error is actually perfect. Like if we follow the error message, we use

ages = {'Alice'==22}

And we actually get a "set" with the first value as False. Sets behaves syntactically like list but have different behaviors of mathematical sets.

I have an idea of what's causing the first one, but the second I am not sure we can detect easily we are in that case. Do you have a suggestion for what to place in the second case?

I'm don't the second is a problem at all. What the error message is suggesting is perfect since it doesn't know if we're trying to use a set or dict.

Sorry for the typos.

I don't know, it think is more likely that people are triying to use the "=" as a ":" and constructing a literal. Is not a bad error, but I think is not the best one

Hmmm... Then is it possible to add an exception where the error message will result in,

SyntaxError: cannot assign to literal here. Maybe you meant ':', "==" or ":=" instead of '='?

only if we're dealing with curly braces?

In the second case, I understand very well that it could have been a set literal. In my (limited) experience, I have never seen a set literal containing a single element obtained from an == comparison.

Since dict can be built by using keyword arguments, I tend to assume that using = in an literal that starts with { is meant to be a dict.

In
>>> ages = {'Alice' = 22}

replacing the equal sign by either ==, :, or a comma would generate no SyntaxError.  Clearly (in my mind anyway, and in previous Python versions), the "bad token" is the equal sign, and not the string Alice.

Here's what I show with friendly:

======
>>> ages = {'Alice'=22}

Traceback (most recent call last):
  File "<friendly-console:1>", line 1
    ages = {'Alice'=22}
                   ^
SyntaxError: invalid syntax
>>> why()

It is possible that you used an equal sign = instead of a colon : to assign values to keys in a dict before or at the
position indicated by ^.

=====
Admitedly, this suggestion could also be wrong - but the focus on this case (imo) should be on the "bad token" shown, which should be the equal sign.

New changeset 07dba474c582e61ca455846da7597d4346324e04 by Miss Islington (bot) in branch '3.10':
bpo-44180: Report generic syntax errors in the furthest position reached in the first parser pass (GH-26253) (GH-26281)
https://github.com/python/cpython/commit/07dba474c582e61ca455846da7597d4346324e04

New changeset ae1732d4611ee859c754e7a867b2a4cbb47d0637 by Miss Islington (bot) in branch '3.10':
bpo-44180: Fix edge cases in invalid assigment rules in the parser (GH-26283)
https://github.com/python/cpython/commit/ae1732d4611ee859c754e7a867b2a4cbb47d0637