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Diffstat (limited to 'Doc/tut/tut.tex')
| -rw-r--r-- | Doc/tut/tut.tex | 24 |
1 files changed, 20 insertions, 4 deletions
diff --git a/Doc/tut/tut.tex b/Doc/tut/tut.tex index 6451e2a..c5a9294 100644 --- a/Doc/tut/tut.tex +++ b/Doc/tut/tut.tex @@ -1755,10 +1755,15 @@ item, then to the result and the next item, and so on. For example, \subsection{List Comprehensions} -List comprehensions provide a concise way to create lists without -resorting to use of the \function{map()} or \function{filter()} -functions. The resulting construct tends often to be clearer than use -of those functions. +List comprehensions provide a concise way to create lists without resorting +to use of \function{map()}, \function{filter()} and/or \keyword{lambda}. +The resulting list definition tends often to be clearer than lists built +using those constructs. Each list comprehension consists of an expression +following by a \keyword{for} clause, then zero or more \keyword{for} or +\keyword{if} clauses. The result will be a list resulting from evaluating +the expression in the context of the \keyword{for} and \keyword{if} clauses +which follow it. If the expression would evaluate to a tuple, it must be +parenthesized. \begin{verbatim} >>> freshfruit = [' banana', ' loganberry ', 'passion fruit '] @@ -1771,6 +1776,17 @@ of those functions. [12, 18] >>> [3*x for x in vec if x < 2] [] +>>> [{x: x**2} for x in vec] +[{2: 4}, {4: 16}, {6: 36}] +>>> [[x,x**2] for x in vec] +[[2, 4], [4, 16], [6, 36]] +>>> [x, x**2 for x in vec] # error - parens required for tuples + File "<stdin>", line 1 + [x, x**2 for x in vec] + ^ +SyntaxError: invalid syntax +>>> [(x, x**2) for x in vec] +[(2, 4), (4, 16), (6, 36)] >>> vec1 = [2, 4, 6] >>> vec2 = [4, 3, -9] >>> [x*y for x in vec1 for y in vec2] |