5.2.4 List displays

A list display is a possibly empty series of expressions enclosed in square brackets:

test	::=	or_test \| lambda_form
testlist	::=	test ( "," test )* [ "," ]
list_display	::=	"[" [listmaker] "]"
listmaker	::=	expression ( list_for \| ( "," expression )* [","] )
list_iter	::=	list_for \| list_if
list_for	::=	"for" expression_list "in" testlist [list_iter]
list_if	::=	"if" test [list_iter]

A list display yields a new list object. Its contents are specified by providing either a list of expressions or a list comprehension. When a comma-separated list of expressions is supplied, its elements are evaluated from left to right and placed into the list object in that order. When a list comprehension is supplied, it consists of a single expression followed by at least one for clause and zero or more for or if clauses. In this case, the elements of the new list are those that would be produced by considering each of the for or if clauses a block, nesting from left to right, and evaluating the expression to produce a list element each time the innermost block is reached^5.1.

Footnotes

... reached ^5.1: In Python 2.3, a list comprehension "leaks" the control variables of each "for" it contains into the containing scope. However, this behavior is deprecated, and relying on it will not work once this bug is fixed in a future release

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