I did it with

    python3 -c "`echo -e 'import time\nwhile True:\n print(u"\u2571\u2572"[int(time.time() * 100)%2],end="")\n time.sleep(0.001)'`"

The neat thing about it is that the randomness comes from the inexactness of time.sleep

You can write it like this:

    python -c "while 1:import sys,random;sys.stdout.write(random.choice('\/'))"

and it's shorter too !

It is a spec. Python in general prefers a statement over an expression, so the while statement does not have an expression form.

Python has two types of statements; "simple" statement and "compound" statements. Compound statements are those, like the if- and while-statements, which require multiple lines.

Only simple statements may be separated by a ';', not compound statements.

This is a bit different than what you wrote. For example, "x=4" is a statement, and not an expression, but "x=4;y=5;z=6" is a valid Python line because assignment is a simple statement, and multiple simple statements may be separated by a ';'.