How to Think Like a Computer Scientist: Learning with Python 2nd Edition/Solutions/CH 10
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Chapter 10[edit | edit source]
CH 10 - Solution 1[edit | edit source]
CH 10 - Solution 1.1[edit | edit source]
>>> import calendar
>>> year = calendar.calendar(2008)
>>> print year
2008
January February March
Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
1 2 3 4 5 6 1 2 3 1 2
7 8 9 10 11 12 13 4 5 6 7 8 9 10 3 4 5 6 7 8 9
14 15 16 17 18 19 20 11 12 13 14 15 16 17 10 11 12 13 14 15 16
21 22 23 24 25 26 27 18 19 20 21 22 23 24 17 18 19 20 21 22 23
28 29 30 31 25 26 27 28 29 24 25 26 27 28 29 30
31
April May June
Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
1 2 3 4 5 6 1 2 3 4 1
7 8 9 10 11 12 13 5 6 7 8 9 10 11 2 3 4 5 6 7 8
14 15 16 17 18 19 20 12 13 14 15 16 17 18 9 10 11 12 13 14 15
21 22 23 24 25 26 27 19 20 21 22 23 24 25 16 17 18 19 20 21 22
28 29 30 26 27 28 29 30 31 23 24 25 26 27 28 29
30
July August September
Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
1 2 3 4 5 6 1 2 3 1 2 3 4 5 6 7
7 8 9 10 11 12 13 4 5 6 7 8 9 10 8 9 10 11 12 13 14
14 15 16 17 18 19 20 11 12 13 14 15 16 17 15 16 17 18 19 20 21
21 22 23 24 25 26 27 18 19 20 21 22 23 24 22 23 24 25 26 27 28
28 29 30 31 25 26 27 28 29 30 31 29 30
October November December
Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
1 2 3 4 5 1 2 1 2 3 4 5 6 7
6 7 8 9 10 11 12 3 4 5 6 7 8 9 8 9 10 11 12 13 14
13 14 15 16 17 18 19 10 11 12 13 14 15 16 15 16 17 18 19 20 21
20 21 22 23 24 25 26 17 18 19 20 21 22 23 22 23 24 25 26 27 28
27 28 29 30 31 24 25 26 27 28 29 30 29 30 31
>>>
CH 10 - Solution 1.2[edit | edit source]
isleap(year) - Return 1 for leap years, 0 for non-leap years.
>>> from calendar import *
>>> isleap(2008)
True
>>> isleap(2009)
False
>>>
CH 10 - Solution 2[edit | edit source]
CH 10 - Solution 2.1[edit | edit source]
python C:\Python26\Lib\pydoc.py -p 7464
CH 10 - Solution 2.2[edit | edit source]
There are 35 functions in the math module.
CH 10 - Solution 2.3[edit | edit source]
The floor function finds the greatest integral value less than or equal to x. The ceil function finds the lowest integeral value greater than or equal to x.
CH 10 - Solution 2.4[edit | edit source]
CH 10 - Solution 2.5[edit | edit source]
The two data constants in the math module are: 'e' and 'pi'.
CH 10 - Solution 3[edit | edit source]
"""
Interface summary:
import copy
x = copy.copy(y) # make a shallow copy of y
x = copy.deepcopy(y) # make a deep copy of y
For module specific errors, copy.Error is raised.
The difference between shallow and deep copying is only relevant for
compound objects (objects that contain other objects, like lists or
class instances).
- A shallow copy constructs a new compound object and then (to the
extent possible) inserts *the same objects* into it that the
original contains.
- A deep copy constructs a new compound object and then, recursively,
inserts *copies* into it of the objects found in the original."""
deepcopy would have come handy in exercises you didn't have to solve regarding object reference, thus no answer is excpected here.
CH 10 - Solution 4[edit | edit source]
CH 10 - Solution 5[edit | edit source]
CH 10 - Solution 6[edit | edit source]
Namespaces are one honking great idea -- let's do more of those!
CH 10 - Solution 7[edit | edit source]
CH 10 - Solution 8[edit | edit source]
def matrix_mult(m1, m2):
"""
>>> matrix_mult([[1, 2], [3, 4]], [[5, 6], [7, 8]])
[[19, 22], [43, 50]]
>>> matrix_mult([[1, 2, 3], [4, 5, 6]], [[7, 8], [9, 1], [2, 3]])
[[31, 19], [85, 55]]
>>> matrix_mult([[7, 8], [9, 1], [2, 3]], [[1, 2, 3], [4, 5, 6]])
[[39, 54, 69], [13, 23, 33], [14, 19, 24]]
"""
qr = len(m1)
qc = len(m2[0])
NewMtx = []
for row in range(qr):
newRow = []
for column in range(qc):
newRow.append(row_times_column(m1, row, m2, column))
NewMtx.append(newRow)
return NewMtx
return NewMtx
qr = len(m1)
qc = len(m2[0])
NewMtx = []
for row in range(qr):
newRow = []
for column in range(qc):
newRow.append(row_times_column(m1, row, m2, column))
NewMtx.append(newRow)
CH 10 - Solution 9[edit | edit source]
CH 10 - Solution 10[edit | edit source]
def myreplace(old, new, s):
"""
Replace all occurences of old with new in the string s.
>>> myreplace(',', ';', 'this, that, and, some, other, thing')
'this; that; and; some; other; thing'
>>> myreplace(' ', '**', 'Words will now be separated by stars.')
'Words**will**now**be**separated**by**stars.'
"""
old_removed = s.split(old)
new_added = new.join(old_removed)
return new_added
# Shorter version
# new_added = new.join(s.split(old))
CH 10 - Solution 11[edit | edit source]
def cleanword(word):
"""
>>> cleanword('what?')
'what'
>>> cleanword('"now!"')
'now'
>>> cleanword('?+="word!,@$()"')
'word'
"""
cleaned_word = ''
for i in range(len(word)):
char = word[i]
if char.isalpha():
cleaned_word += char
return cleaned_word
def has_dashdash(s):
"""
>>> has_dashdash('distance--but')
True
>>> has_dashdash('several')
False
>>> has_dashdash('critters')
False
>>> has_dashdash('spoke--fancy')
True
>>> has_dashdash('yo-yo')
False
"""
return s.find('--') != -1
def extract_words(s):
"""
>>> extract_words('Now is the time! "Now", is the time? Yes, now.')
['now', 'is', 'the', 'time', 'now', 'is', 'the', 'time', 'yes', 'now']
>>> extract_words('she tried to curtsey as she spoke--fancy')
['she', 'tried', 'to', 'curtsey', 'as', 'she', 'spoke', 'fancy']
"""
if has_dashdash(s):
s = myreplace('--', ' ', s) #using myreplace function from Q. 10
words_punc = s.split()
cleanlist = []
for word in words_punc:
cleanedword = cleanword(word).lower()
cleanlist.append(cleanedword)
return cleanlist
def wordcount(word, wordlist):
"""
>>> wordcount('now', ['now', 'is', 'time', 'is', 'now', 'is', 'is'])
['now', 2]
>>> wordcount('is', ['now', 'is', 'time', 'is', 'now', 'is', 'the', 'is'])
['is', 4]
>>> wordcount('time', ['now', 'is', 'time', 'is', 'now', 'is', 'is'])
['time', 1]
>>> wordcount('frog', ['now', 'is', 'time', 'is', 'now', 'is', 'is'])
['frog', 0]
"""
return [word, wordlist.count(word)]
def wordset(wordlist):
"""
>>> wordset(['now', 'is', 'time', 'is', 'now', 'is', 'is'])
['is', 'now', 'time']
>>> wordset(['I', 'a', 'a', 'is', 'a', 'is', 'I', 'am'])
['I', 'a', 'am', 'is']
>>> wordset(['or', 'a', 'am', 'is', 'are', 'be', 'but', 'am'])
['a', 'am', 'are', 'be', 'but', 'is', 'or']
"""
for word in wordlist:
count = wordcount(word, wordlist)[1]
if count > 1:
for a in range(count - 1):
wordlist.remove(word)
wordlist.sort()
return wordlist
def longestword(wordset):
"""
>>> longestword(['a', 'apple', 'pear', 'grape'])
5
>>> longestword(['a', 'am', 'I', 'be'])
2
>>> longestword(['this', 'that', 'supercalifragilisticexpialidocious'])
34
"""
longest = 0
for word in wordset:
length = len(word)
if length > longest:
longest = length
return longest
if __name__ == '__main__':
import doctest
doctest.testmod()
CH 10 - Solution 12[edit | edit source]
#sort_fruits.py
source = open('unsorted_fruits.txt', 'r')
fruits = source.readlines()
source.close()
fruits.sort()
newfile = open('sorted_fruits.txt', 'w')
newfile.writelines(fruits)
newfile.close()
CH 10 - Solution 13[edit | edit source]
CH 10 - Solution 14[edit | edit source]
#mean.py
from sys import argv
nums = argv[1:]
for i, value in enumerate(nums):
nums[i] = float(value)
mean = sum(nums) / len(nums)
print mean
CH 10 - Solution 15[edit | edit source]
#median.py
from sys import argv
nums = argv[1:]
for i, value in enumerate(nums):
nums[i] = float(value)
nums.sort()
size = len(nums)
middle = size / 2
if size % 2 == 0:
median = (nums[middle - 1] + nums[middle]) / 2
else:
median = nums[middle]
if median == float(int(median)):
median = int(median)
print median
CH 10 - Solution 16[edit | edit source]
#
# countletters.py
#
def display(i):
if i == 10: return 'LF'
if i == 13: return 'CR'
if i == 32: return 'SPACE'
return chr(i)
from sys import argv
filename = argv[1]
infile = open(filename, 'r')
text = infile.read()
infile.close()
counts = 128 * [0]
for letter in text:
counts[ord(letter)] += 1
filenamesplit = filename.split('.') # splits 'name.txt' -> ['name', 'txt']
count_file = filenamesplit[0] + '_counts.dat' # 'name' -> 'name_counts.dat'
outfile = open(count_file, 'w')
outfile.write("%-12s%s\n" % ("Character", "Count"))
outfile.write("=================\n")
for i in range(len(counts)):
if counts[i]:
outfile.write("%-12s%d\n" % (display(i), counts[i]))
outfile.close()