Learning about dictionaries

[Thomas Philips]

I'm teaching myself python and in the course of playing around with
dictionaries, I tried to create the following trivial dictionary

{1:'one', 2:'two'}

So I entered
>>> dict(1='one',2='two')
SyntaxError: keyword can't be an expression

As this did not work, I tried
>>> dict(1=one,2=two)
SyntaxError: keyword can't be an expression

and
>>> dict('1'='one','2'='two')
SyntaxError: keyword can't be an expression

as well as
>>> dict('1'=one,'2'=two)
SyntaxError: keyword can't be an expression

Out of curiosity, I tried
>>> dict(one=1,two=2)
{'two': 2, 'one': 1}

Why does this last attempt work, and more importantly, why did my four
earlier attempts fail? I might add that I have no trouble getting what
I want with
>>> dict(zip((1,2),('one','two')))
{1: 'one', 2: 'two'}
or
>>> dict(((1,'one'),(2,'two')))
{1: 'one', 2: 'two'}

Sincerely

Thomas Philips