# If you ever wanted to do something like:
for line in open('file').readlines().reverse():
print line
# you will have noticed that reverse is an "In-Place" method.
# it modifies the list itself and returns None.
# So the for loop sees just a (non-iterable) None.
# Even worse, you can't use reverse/sort/extend on tuples or strings.
# "hallo".reverse() or (3,1,5).sort() does not exist.
# The obfuscated oneliner below solves these problems so that
# you can write
for line in reverse(open('file').readlines()):
print line # lines of the file in reverse order
# Additionally it allows you to use reverse/sort/extend
# on tuples and strings and it always maintains Types.
sort([3,7,5]) # gives you a sorted list [3,5,7]
reverse("hallo") # returns reversed string "ollah"
extend( (1,2,3), (4,5) ) # returns (1,2,3,4,5)
# recursion/iteration of course works like usual:
print reverse(sort([7,3,5])) # prints [7,5,3]
print extend(reverse(range(4)),([42],reverse('32')))
# will give you [3, 2, 1, 0, [42], '23']
# the last line shows, that types are really preserved!
# OK. Now on to the actual "Oneliner". I told you it's obfuscated
# so don't complain. It actually has 275 characters so i
# split it here in four lines to make it (hopefully) "pastable"
for n,m in ( ('reverse(o)','n.reverse()'),('sort(o)','n.sort()'),\
('extend(o,o1)','n.extend(o1)')): exec "def %s:\n t=type\n to=t(o)\
\n if to in (t(''),t(())): n=list(o)\n else: n=to(o)\n %s\n return n and\
(to==t('') and ''.join(n) or to==t(()) and tuple(n) or n) or to()\n" % (n,m)
# paste this code into your interpreter or module
# and the above examples should work. If you are interested in how
# it basically works (i hope so:-) read on
################
# Obviously you don't want me to talk about this code in compact form...
# (I have put an easily readable version at the end of the page)
# How does it work?
# It actually puts three functions into your current namespace.
# Let me show you the first one, "reverse"
def reverse(o):
t=type # shortcut
to=t(o) # store type of object to be reversed
if to in (t(''),t(())): n=list(o) # for tuples and strings construct list
else: n=to(o) # otherwise call copy-constructor
n.reverse() # now call the inplace method
return n and (to==t('') and ''.join(n) or to==t(()) and tuple(n) or n) or to()
# The last line ensures that the result is of the same type as the input
# and that Results with length 0 are correctly returned.
# Actually reverse does not only work on strings, tuples and lists.
# It also works on any object which has an "Inplace-" reverse method,
# a copy constructor and has the conversion into bool.
# the generated "sort"-method is - apart from name - exactly like reverse.
# But "extend" is different because it needs another argument!
# If you look in the "for ... :"-part of the onliner you will
# see that "extend" comes out slightly differently:
def extend(o,o1): # NOTE THIS LINE
t=type
to=t(o)
if to in (t(''),t(())): n=list(o)
else: n=to(o)
n.extend(o1) # NOTE THIS LINE
return n and (to==t('') and ''.join(n) or to==t(()) and tuple(n) or n) or to()
# but actually it differs only in number of arguments:
# - def extend(o,o1): has two arguments
# - n.extend(o1) gets the second argument
# If you want to play with it you should really use
# the following "longish" version of the code and put it in a module.
signatures = (('reverse(o)','n.reverse()'),\
('sort(o)','n.sort()'), \
('extend(o,o1)','n.extend(o1)'))
functemplate="""
def %s:
t=type
to=t(o)
if to in (t(''),t(())):
n=list(o)
else:
n=to(o)
%s
return n and (to==t('') and ''.join(n) or to==t(()) and tuple(n) or n) or to()
"""
for n,m in signatures:
#print functemplate % (n,m) # remove comment if you want to see
exec functemplate % (n,m)
