more flexibility in the var= << operator

[edublancas]

in #501 var= << was introduced to print the data frame while assigning it. However, it's too strict and we should allow other versions to have the same effect. Essentially, we should ignore the space surrounding the =, just like f-strings in Python:【 code pythoh 】

In [4]: x = 'hello'

In [5]: f"{x=}"

Out[5]: "x='hello'"

In [6]: f"{x =}"

Out[6]: "x ='hello'"

In [7]: f"{x = }"

Out[7]: "x = 'hello'"

In [8]: f"{x}"

Out[8]: 'hello'

In [9]: f"{x = }"

Out[9]: "x = 'hello'"

【 end code 】