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I Am Legend
01-30-2012, 06:30 AM
Ive been trying to do this



#!/usr/bin/python -tt
# Copyright 2010 Google Inc.
# Licensed under the Apache License, Version 2.0
# http://www.apache.org/licenses/LICENSE-2.0

# Google's Python Class
# http://code.google.com/edu/languages/google-python-class/

# Basic list exercises
# Fill in the code for the functions below. main() is already set up
# to call the functions with a few different inputs,
# printing 'OK' when each function is correct.
# The starter code for each function includes a 'return'
# which is just a placeholder for your code.
# It's ok if you do not complete all the functions, and there
# are some additional functions to try in list2.py.

# A. match_ends
# Given a list of strings, return the count of the number of
# strings where the string length is 2 or more and the first
# and last chars of the string are the same.
# Note: python does not have a ++ operator, but += works.
def match_ends(words):

count = 0
for num in words:

if len(num) > 0:
first = num[0]
second = num[-1]



if len(num) >= 2:
if (first == second):
count += 1
# +++your code here+++
return count


# B. front_x
# Given a list of strings, return a list with the strings
# in sorted order, except group all the strings that begin with 'x' first.
# e.g. ['mix', 'xyz', 'apple', 'xanadu', 'aardvark'] yields
# ['xanadu', 'xyz', 'aardvark', 'apple', 'mix']
# Hint: this can be done by making 2 lists and sorting each of them
# before combining them.
def front_x(words):
array1 = []
array2 = words

for findx in words:

if (findx[0] == 'x'):
array1.append(findx)
array2.remove(findx)


array1.sort()
array2.sort()
array1.extend(array2)




# print array1,array2,words,findx





return array1



# C. sort_last
# Given a list of non-empty tuples, return a list sorted in increasing
# order by the last element in each tuple.
# e.g. [(1, 7), (1, 3), (3, 4, 5), (2, 2)] yields
# [(2, 2), (1, 3), (3, 4, 5), (1, 7)]
# Hint: use a custom key= function to extract the last element form each tuple.
def sort_last(tuples):
# +++your code here+++
return


# Simple provided test() function used in main() to print
# what each function returns vs. what it's supposed to return.
def test(got, expected):
if got == expected:
prefix = ' OK '
else:
prefix = ' X '
print '%s got: %s expected: %s' % (prefix, repr(got), repr(expected))


# Calls the above functions with interesting inputs.
def main():
print 'match_ends'
test(match_ends(['aba', 'xyz', 'aa', 'x', 'bbb']), 3)
test(match_ends(['', 'x', 'xy', 'xyx', 'xx']), 2)
test(match_ends(['aaa', 'be', 'abc', 'hello']), 1)

print
print 'front_x'
test(front_x(['bbb', 'ccc', 'axx', 'xzz', 'xaa']),
['xaa', 'xzz', 'axx', 'bbb', 'ccc'])
test(front_x(['ccc', 'bbb', 'aaa', 'xcc', 'xaa']),
['xaa', 'xcc', 'aaa', 'bbb', 'ccc'])
test(front_x(['mix', 'xyz', 'apple', 'xanadu', 'aardvark']),
['xanadu', 'xyz', 'aardvark', 'apple', 'mix'])


print
print 'sort_last'
test(sort_last([(1, 3), (3, 2), (2, 1)]),
[(2, 1), (3, 2), (1, 3)])
test(sort_last([(2, 3), (1, 2), (3, 1)]),
[(3, 1), (1, 2), (2, 3)])
test(sort_last([(1, 7), (1, 3), (3, 4, 5), (2, 2)]),
[(2, 2), (1, 3), (3, 4, 5), (1, 7)])


if __name__ == '__main__':
main()



But for some reasons it seems to skip 'xaa' in the list array in the for loop right after once executing the if statement so please help me

mixster
01-30-2012, 11:01 AM
Change
array2 = words
to
array2 = words[:]

In Python, you have mutable datatypes and immutable datatypes. A mutable datatype means that when you do "x = y" and then change y you will also change x. An immutable datatype doesn't do this, so doing "x = y" and then changing y will not change x. A list - declared as x = [] - is a mutable type, while a tuple - declared as x = () - is not. Since words is a list, when you do array2 = words and then, in the loop, do array2.remove(findx), you're also removing entries from words, so the for loop terminates prematurely.

Happy Pythoning!

I Am Legend
01-31-2012, 09:52 AM
thanks brother makes sense :)