∫
is Unicode's U+222B. Depending on your platform, this can be input in various ways. For example :
On most Linux's terminals, Ctrl-Shift-U + 222B, then <space> will input ∫.
Emac's input method "TeX" allows you to type "\int" to get ∫.
But this character isn't accepted by Python as an identifier ; you can't use it as a synonym to integrate
:
sage: ∫=integrate
Input In [4]
∫=integrate
^
SyntaxError: invalid character '∫' (U+222B)
Furthermore, this example illustrates that displaying ∫(sin(x), (x, 0,π))
isn't really an acceptable substutite to $\displaystyle{\int_0^\pi\sin(x) \operatorname{d}\!x}$ : the substitute is hard to read and ugly as hell...
What you seem to aim at is an input mechanism accepting your keystrokes/mousestrokes , using them to build a structure representing some mathematical expression and displaying a "nice" visual representation of it. That's what Matehmatica interface does.
Such an input interpreter is probably somewhat lateral to Sage's goals... I have found that Sage's ability to latex
any Sage object is enough (and easy enough to use) to check and understand anything I have had to use...
HTH,
EDIT : as noted by @tolga, this answer to a previous question is relevant : it suggests to use Sage through TeXmacs, thus benefitting of TeXmacs interface. Which I don't know...
This can be somehow related with https://ask.sagemath.org/question/541...