@@ -809,16 +809,12 @@ and can be used as a key for a dictionary.
809809
810810One peculiarity of Python that can surprise beginners is that
811811strings are immutable. This means that when constructing a string from
812- its parts, it is much more efficient to accumulate the parts in a list,
813- which is mutable, and then glue ('join') the parts together when the
814- full string is needed. One thing to notice, however, is that list
815- comprehensions are better and faster than constructing a list in a loop
816- with calls to ``append() ``.
817-
818- One other option is using the map function, which can 'map' a function
819- ('str') to an iterable ('range(20)'). This results in a map object,
820- which you can then ('join') together just like the other examples.
821- The map function can be even faster than a list comprehension in some cases.
812+ its parts, appending each part to the string is inefficient because
813+ the entirety of the string is copied on each append.
814+ Instead, it is much more efficient to accumulate the parts in a list,
815+ which is mutable, and then glue (``join ``) the parts together when the
816+ full string is needed. List comprehensions are usually the fastest and
817+ most idiomatic way to do this.
822818
823819**Bad **
824820
@@ -830,7 +826,7 @@ The map function can be even faster than a list comprehension in some cases.
830826 nums+= str (n)# slow and inefficient
831827print nums
832828
833- Good **
829+ Better **
834830
835831..code-block ::python
836832
@@ -840,20 +836,12 @@ The map function can be even faster than a list comprehension in some cases.
840836 nums.append(str (n))
841837print " " # much more efficient
842838
843- Better **
844-
845- ..code-block ::python
846-
847- # create a concatenated string from 0 to 19 (e.g. "012..1819")
848- nums= [str (n)for nin range (20 )]
849- print " "
850-
851839Best **
852840
853841..code-block ::python
854842
855843# create a concatenated string from 0 to 19 (e.g. "012..1819")
856- nums= map ( str , range (20 ))
844+ nums= [ str (n) for n in range (20 )]
857845print " "
858846
859847join() `` is not always