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(python2.1-ref.info)List displays

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

     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.