why expression [code] is accepted by python? what is origin of that?

Question

I wrote this expression

[0 for j in range(4)]

and python accepted it as definition of list, but when i wrote this expression:

0 for j in range(4)

it raises an error.

what is mechanism of that and from which language does it origin? is it from functional programming ie. LISP? What is equivalent in Java or C?

EDIT: the difference from answered question is that there is not left part of equitation, just right part

[code]

Also I was interested in origin of list comprehension and equivalents in other programming languages.

Note that you can create a *generator expression* with parentheses: `(0 for j in range(4))`. — jonrsharpe, Oct 06 '15 at 14:40
And the PEP that defined the syntax: https://www.python.org/dev/peps/pep-0202/ — Martijn Pieters, Oct 06 '15 at 14:42
@AshwiniChaudhary: I'm not sure that the Python developers took it from Haskell directly. The concept and name existed in NPL already, see https://en.wikipedia.org/wiki/List_comprehension — Martijn Pieters, Oct 06 '15 at 14:43
@MartijnPieters https://docs.python.org/3/whatsnew/2.0.html#list-comprehensions Though it's hard to say Greg Ewing was thinking of Haskell when he added the related patches. — Ashwini Chaudhary, Oct 06 '15 at 14:53
@jonrsharpe what is result of that expression, i get generator and can't print it. — user1406647, Oct 06 '15 at 20:32
A generator *is* the result of that expression! If you want to see what it contains, you need to *consume it* by iterating over it. — jonrsharpe, Oct 06 '15 at 20:33

score 2 · Answer 1 · answered Oct 06 '15 at 14:39

2

[0 for j in range(4)] is a list comprehension. This is perfectly valid Python syntax.

The other expression isn't an expression at all.

answered Oct 06 '15 at 14:39

Makoto

1 Answers1