## Chapter 1

See below for Chapter 1 exercises.

### Exercise 1.2

3.) If you run a 10 kilometer race in 42 minutes 42 seconds, what is your average time per mile? What is your average speed in miles per hour? (Hint: there are about 1.61 kilometers in a mile.)

>>> 10 / 1.61 # convert kilometers to miles

6.211180124223602

>>> (42 * 60) + 42 # convert time to seconds

2562

>>> 2562 / 6.211180124223602 # what is your average time (seconds) per mile

412.482

>>> 412.482 / 60 # what is your average time (minutes) per mile

6.874700000000001

>>> 60 / 6.874700000000001 # miles per hour

8.727653570337614

>>> 10 / 42.7 # avg kilometers per minute

0.23419203747072598

>>> 0.23419203747072598 * 60 # kilometers per hour

14.05152224824356

>>> 14.05152224824356 / 1.61 # convert to M.P.H

8.727653570337614

or a one-liner

>>> (10 / 1.61) / (42.7 / 60) # (distance in miles) / (time in hours)

8.727653570337614 # miles/hour

## Chapter 2

### Exercise 2.1

If you type an integer with a leading zero, you might get a confusing error:

```>>> zipcode = 02492
^
SyntaxError: invalid token
```

Other number seem to work, but the results are bizarre:

```>>> zipcode = 02132
>>> print zipcode
1114
```

So python is assuming you want to convert an octal number to a decimal number. In the base 8 numbering system where valid numbers are 0, 1, 2, 3, 4, 5, 6 and 7.

```Base  8: 00 01 02 03 04 05 06 07 10 11 12 13 14 15 16 17 20 21 22 23 24
Base 10: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20
```

Every 8 numbers we increment the left hand columns. This means that the right most column is the number of 'ones'. The one to the left of that is a tally of the number of 'eights', the one next to that is a tally of a full column of 'eight' times the 'eight column' - 64. The one next to that is 64*8 - 512 and so on. For more information read Base Eight math.

That is why zipcode = 02492 is invalid as the digit 9 is not a valid octal number. We can do the conversion manually as follows:

```>>> print 02132
1114
>>> (2*512)+(1*64)+(3*8)+(2*1)
1114
>>>
```

### Exercise 2.2

The volume of a sphere with radius r is 4/3 π r3. What is the volume of a sphere with radius 5?

```>>> pi = 3.1415926535897932
>>> r = 5
>>> 4/3*pi*r**3 # This is the wrong answer
392.69908169872411
>>> r = 5.0 # Radius can be a float here as well, but is not _necessary_.
>>> 4.0/3.0*pi*r**3 # Using floats give the correct answer
523.5987755982989
>>>
```

Suppose the cover price of a book is \$24.95, but bookstores get a 40% discount. Shipping costs \$3 for the first copy and 75 cents for each additional copy. What is the total wholesale cost for 60 copies?

``` \$24.95  Cost
\$9.98  Discount per book
\$14.97  Cost per book after discount
60     Total number of books
\$898.20  Total cost not inc delivery

\$3.00  First book delivery
59     Remaining books
\$0.75  Delivery cost for extra books
\$44.25  Total cost for extra books
\$47.25  Total Delivery cost

\$945.45	 Total Bill

This answer is wrong because 40.0/100.0 return wrong value 0.40000000000000002 for more info see IEEE 754 (Standard for Floating-Point Arithmetic)
>>> (24.95-24.95*40.0/100.0)*60+3+0.75*(60-1)
945.44999999999993
>>> 24.95*0.6*60+0.75*(60-1)+3
945.45

You can use the decimal module to maintain precision.
from decimal import Decimal
..
...
def wholesale_cost(args):

d = 1 - args.get('discount')/100
purchase = Decimal(args.get('cost') * d * 60)
return purchase + Decimal(args.get('delivery'))

args =  {'cost': 24.95, 'discount': 40, 'delivery': 3.00+0.75*59}
```

Another solution using functions as well as input prompts:

```# Total wholesale book cost calculator
cover_price = 24.95

number_of_books = int(input("How many books do you want to order at wholesale? "))

def ship_cost (number_of_books):
if number_of_books == 1:
return (number_of_books * 3) # Cost of shipping one book is \$3
else:
return (3 + (number_of_books - 1) * 0.75) # Each additional copy of the book is \$0.75 to ship

def discounted_price(number_of_books):
return(cover_price - (cover_price * .4)) # There is a 40% discount on wholesale book sales

def wholesale_cost(number_of_books):
return ((discounted_price(number_of_books) * number_of_books) + ship_cost(number_of_books))

print("The cost of buying and shipping", number_of_books, "books is \$",round(wholesale_cost(number_of_books), 2))
```

If I leave my house at 6:52 am and run 1 mile at an easy pace (8:15 per mile), then 3 miles at tempo (7:12 per mile) and 1 mile at easy pace again, what time do I get home for breakfast?

How I did it:

```>>> start = (6*60+52)*60
>>> easy = (8*60+15)*2
>>> fast = (7*60+12)*3
>>> finish_hour = (start + easy + fast)/(60*60.0)
>>> finish_floored = (start + easy + fast)//(60*60)  #int() function can also be used to get integer value, but isn't taught yet.
>>> finish_minute  = (finish_hour - finish_floored)*60
>>> print ('Finish time was %d:%d' % (finish_hour,finish_minute))
Finish time was 7:30

*** ANOTHER WAY ***
start_time_hr = 6 + 52 / 60.0
easy_pace_hr = (8 + 15 / 60.0 ) / 60.0
tempo_pace_hr = (7 + 12 / 60.0) / 60.0
running_time_hr = 2 * easy_pace_hr + 3 * tempo_pace_hr
breakfast_hr = start_time_hr + running_time_hr
breakfast_min = (breakfast_hr-int(breakfast_hr))*60
breakfast_sec= (breakfast_min-int(breakfast_min))*60

print ('breakfast_hr', int(breakfast_hr) )
print ('breakfast_min', int (breakfast_min) )
print ('breakfast_sec', int (breakfast_sec) )
>>>
```

## Chapter 3

### Exercise 3.1

Python provides a built-in function called len that returns the length of a string, so the value of len('allen') is 5. Write a function named right_justify that takes a string named s as a parameter and prints the string with enough leading spaces so that the last letter of the string is in column 70 of the display.

```>>> def right_justify(s):
print (' '*(70-len(s))+s)

>>> right_justify('allen')
allen
>>>
```

Alternate Solution Using concatenation and repetition

```def right_justify(s):
total_length = 70
current_length = len(s)
current_string = s
while current_length < total_length:
current_string = " " + current_string
current_length = len(current_string)
print(current_string)

OUTPUT

>>> right_justify("monty")
monty
```

### Exercise 3.3

You can see my solution at http://thinkpython.com/code/grid.py.

```"""
Solution to Exercise 3.5 on page 27 of Think Python
Allen B. Downey, Version 1.1.24+Kart [Python 3.2]

"""

# here is a mostly-straightforward solution to the
# two-by-two version of the grid.

def do_twice(f):
f()
f()

def do_four(f):
do_twice(f)
do_twice(f)

def print_beam():
print('+ - - - -', end='')

def print_post():
print('|        ', end='')

def print_beams():
do_twice(print_beam)
print('+')

def print_posts():
do_twice(print_post)
print('|')

def print_row():
print_beams()
do_twice(print_posts)

def print_grid():
do_twice(print_row)
print_beams()

print_grid()
____________

# another solution

def do_twice(f):
f()
f()

def do_four(f):
do_twice(f)
do_twice(f)

def print_column():
print '+----+----+'

def print_row():
print '|    |    |'

def print_rows():
do_four(print_row)

def do_block():
print_column()
print_rows()

def print_block():
do_twice(do_block)
print_column()

print_block()

# nathan moses-gonzales
_________

# straight-forward solution to 4x4 grid

def do_twice(f):
f()
f()

def do_four(f): # not needed for 2x2 grid
do_twice(f)
do_twice(f)

def print_beam():
print('+----', end='')

def print_post():
print('|    ', end='')

def print_beams():
do_twice(print_beam)
print('+')

def print_posts():
do_twice(print_post)
print('|')

def print_row():
print_beams()
do_twice(print_posts)

def print_grid2x2():
do_twice(print_row)
print_beams()

def print_beam4():
do_four(print_beam)
print('+')

def print_post4():
do_four(print_post)
print('|')

def print_row4():
print_beam4()
do_twice(print_post4)

def print_grid4x4():
do_four(print_row4)
print_beam4()

print_grid4x4()
-----------------------

# here is a less-straightforward solution to the
# four-by-four grid

def one_four_one(f, g, h):
f()
do_four(g)
h()

def print_plus():
print '+',

def print_dash():
print '-',

def print_bar():
print '|',

def print_space():
print ' ',

def print_end():
print

def nothing():
"do nothing"

def print1beam():
one_four_one(nothing, print_dash, print_plus)

def print1post():
one_four_one(nothing, print_space, print_bar)

def print4beams():
one_four_one(print_plus, print1beam, print_end)

def print4posts():
one_four_one(print_bar, print1post, print_end)

def print_row():
one_four_one(nothing, print4posts, print4beams)

def print_grid():
one_four_one(print4beams, print_row, nothing)

print_grid()

comment = """
After writing a draft of the 4x4 grid, I noticed that many of the
functions had the same structure: they would do something, do
something else four times, and then do something else once.

So I wrote one_four_one, which takes three functions as arguments; it
calls the first one once, then uses do_four to call the second one
four times, then calls the third.

Then I rewrote print1beam, print1post, print4beams, print4posts,
print_row and print_grid using one_four_one.

Programming is an exploratory process.  Writing a draft of a program
often gives you insight into the problem, which might lead you to
rewrite the code to reflect the structure of the solution.

--- Allen
"""

print comment

# another solution
def beam():
plus = "+"
minus = "-"*4
print(plus, minus, plus,minus, plus, minus, plus, minus, plus)

def straight():
straight = "|"
space = " "*4
print(straight, space, straight, space, straight, space, straight, space,
straight, space)

straight()
straight()
straight()
straight()

def twice():
beam()
beam()

twice()
twice()
beam()

-- :)
------------------

# Without functions.
print("+ - - - - " * 2 + "+")
print("|\t\t  | \t\t|\n" * 3 + "|\t\t  | \t\t|")
print("+ - - - - " * 2 + "+")
print("|\t\t  | \t\t|\n " *3 + "|\t\t  | \t\t|")
print("+ - - - - " * 2 + "+")

------------------

Why not using the first solution and adapt it to the number of rows

def do_twice(f):
f()
f()

def do_four(f):
do_twice(f)
do_twice(f)

def print_column():
print '+----+----+----+----+'

def print_row():
print '|    |    |    |    |'

def print_rows():
do_four(print_row)

def do_block():
print_column()
print_rows()

def print_block():
do_twice(do_block)
# print_column()
do_twice(do_block)
print_column()

print_block()

-----------------------
# mteodor

def draw_line(bar, middle = ' ', repeat = 2, lenght = 2):
""" Draw a single line like this:
[ (B M*repeat)*lenght B]
"""
for k in range(lenght):
print("%s %s " % (bar, middle*repeat), end='')
print(bar)

def draw_grid(lenght = 2, height = 2, width = 2):
""" Draw a grid like this:
+ -- + -- +
|    |    |
|    |    |
+ -- + -- +
|    |    |
|    |    |
+ -- + -- +
where:
* lenght x heigth are the table size
* width is the size of a cell/column
"""
for i in range(height):
draw_line('+', '-', width, lenght)
for j in range(lenght):
draw_line('|', ' ', width, lenght)
draw_line('+', '-', width, lenght)

draw_grid(4, 4, 3)

--------------------------
#kipp

# auto adjust size of columns

size=4

def beam():
print(" + - - - -"*size, "+")

def post():
print(" |        "*size, "|")

def repeat(func):
func()
func()
func()

# manual adjust size for rows
# this is 4

beam()
repeat(post)
beam()
repeat(post)
beam()
repeat(post)
beam()
repeat(post)
beam()
```

## Chapter 4

### 4.3 Exercise 1

```from TurtleWorld import *

world = TurtleWorld()
bob = Turtle()

def square(t):
for i in range(4):
fd(t, 100)
lt(t)

square(bob)
wait_for_user()
```

### 4.3 Exercise 2

```from TurtleWorld import *

world = TurtleWorld()
bob = Turtle()
print(bob)

def square(t, length):
t = Turtle()
for i in range(4):
fd(t, length)
lt(t)

square(bob, 200)
wait_for_user()
```

### 4.3 Exercise 3

```from swampy.TurtleWorld import *

world = TurtleWorld()
bob = Turtle()
print(bob)

def polygon(t, length, n):

for i in range(n):
fd(t, length)
lt(t, 360 / n)

polygon(bob, 50, 8)
wait_for_user()
```

## Chapter 5

### Exercise 5.2

```def countdown(a):         # A typical countdown function
if a < 0:
print("Blastoff")
elif a > 0:
print(a)
countdown(a - 1)

def call_function(n,a):    # The countdown function is called "n" number of times. Any other function can be used instead of countdown function.
for i in range(n):
countdown(a)

call_function(3, 10)
```

### Exercise 5.3

```Def is_triangle(a, b, c):
if a <= b+c:
if b <= a+c:
if c <= a+b:
return 'yes'
else:
return 'no'
else:
return 'no'
else:
return 'no'

is_triangle(1, 12, 1)
'no'
```

### Exercise 5.3

```Def is_triangle(a, b, c):
if a<=b+c and b<=a+c and c<=a+b:
return 'yes'
else:
return 'no'

is_triangle(1, 12, 3)
'no'
```

## Chapter 9

### Exercise 9.1

```fin = open('words.txt')
for line in fin:
word = line.strip()
if len(word) > 20:
print (word)
```

### Exercise 9.2

```fin = open('words.txt')

def has_no_e(word):
for char in word:
if char in 'Ee':
return False
return True

count = 0
for line in fin:
word = line.strip()
if has_no_e(word):
count += 1
print (word)

percent = (count / 113809.0) * 100

print (str(percent)) + "% of the words don't have an 'e'."
```

### Exercise 9.3

```fin = open('words.txt')

def avoids(word,letter):
for char in word:
if char in letter:
return False
return True

letter = raw_input('What letters to exclude? ')
count = 0
for line in fin:
word = line.strip()
if avoids(word, letter):
count += 1
print word

percent = (count / 113809.0) * 100

print str(percent) + "% of the words don't have " + letter + '.'
```

### Exercise 9.4

```def uses_only(word, letters):
"""returns true if word is made only out of letters  else flase"""
for letter in word:
if letter not in letters:
return False
return True
```

## Chapter 10

### Exercise 10.1

Write a function called nested_sum that takes a nested list of integers and add up the elements from all of the nested lists.

```def nested_sum(nestedList):
'''
nestedList: list composed of nested lists containing int.
Returns the sum of all the int in the nested list
'''
newList = []
#Helper function to flatten the list
def flatlist(nestedList):
'''
Returns a flat list
'''
for i in range(len(nestedList)):
if type(nestedList[i]) == int:
newList.append(nestedList[i])
else:
flatlist(nestedList[i])
return newList

flatlist(nestedList)
print sum(newList)

nested_sum(nestedList)
```

### Exercise 10.2

Write a function named "capitalize_nested" that takes a nested list of strings and returns a new nested list with all strings capitalized.

```>>> def capitalize_nested(l):
def capitalize(s):
return s.capitalize()
for n, i in enumerate(l):
if type(i) is list:
l[n] = capitalize_nested(l[n])
elif type(i) is str:
l[n] = capitalize(i)
return l
```

### Exercise 10.3

Write a function that takes a list of numbers and returns the cumulative sum.

```>>> def cumulative(l):
cumulative_sum = 0
new_list = []
for i in l:
cumulative_sum += i
new_list.append(cumulative_sum)
return new_list
```

### Exercise 10.4

Write a function called middle that takes a list and returns a new list that contains all but the first and last elements.

```>>> def middle(x):
res = []
i = 1
while i <= len(x)-2:
res.append(x[i])
i += 1
return res
```

This can also be done simply with a slice.

```>>> def middle(x):
return x[1:-1]
```

### Exercise 10.5

Write a function called chop that takes a list and modifies it, removing the first and last elements, and returns None.

```>>> def chop(x):
del x[:1]
del x[-1:]
```

## Chapter 11

### Exercise 11.1

Write a function that reads the words in words.txt and stores them as keys in a dictionary. It doesn’t matter what the values are. Then you can use the in operator as a fast way to check whether a string is in the dictionary.

```fin = open('words.txt')
englishdict = dict()

def create_diction():
counter = 0
dictionairy = dict()
for line in fin:
word = line.strip()
dictionairy[word] = counter
counter += 1
return dictionairy
```

### Exercise 11.2

```def invert_dict(s):
i={}
for key in s:
v=s[key]
i.setdefault(v, []).append(key)
return i
```

Edit: This was not the exercise I found in my edition of 'Think Python', so I've added my answer in case anyone else is curious: Use get to write histogram more concisely. You should be able to eliminate the if statement.

```def histogram(s):
d = dict()
for c in s:
d[c] = d.get(c,0)+1
return d
```

### Exercise 11.3

Dictionaries have a method called keys that returns the keys of the dictionary, in no particular order, as a list. Modify print_hist to print the keys and their values in alphabetical order.

```v = {'p' : 1, 'a' : 1, 'r' : 2, 'o' : 1, 't' : 1}
def print_hist(h):
d = []
d += sorted(h.keys())
for c in d:
print(c, h[c])
```

OR

```v = {'p' : 1, 'a' : 1, 'r' : 2, 'o' : 1, 't' : 1}
def print_hist(h):
for c in sorted(h.keys()):
print c, h[c]
```

### Exercise 11.4

Modify reverse_lookup so that it builds and returns a list of all keys that map to v, or an empty list if there are none.

```def reverse_lookup(d,v):
l = list()
for c in d:
if d[c] == v:
l.append(c)
return l
```

## Chapter 12

### Exercise 12.1

```numbers = (1,2,3)
def sumall(numbers):
x = 0
for i in numbers:
x = x + i
print x
sumall(numbers)
```

or

```def sumall(*t):
x = 0
for i in range(len(t)):
x += t[i]
return x
```

or

```def sumall(*args):
t = list(args)
return sum(t)
```

or

```def sumall(*args):
return sum(args)
```

### Exercise 12.2

```import random

def sort_by_length(words):
t = []
for word in words:
t.append((len(word),word))
t.sort(reverse=True)
res = []
for length, word in t:
res.append(word)
i=0
final = []
while i <= len(res)-2:
if len(res[i]) == len(res[i+1]):
y_list = [res[i], res[i+1]]
random.shuffle(y_list)
final = final + y_list
i += 2
else:
final.append(res[i])
i += 1
if i == len(res)-1:
final.append(res[i])
return final
```

or

```from random import shuffle

def sort_by_length(words):
r = []
d = dict()
for word in words:
d.setdefault(len(word), []).append(word)
for key in sorted(d, reverse=True):
if len(d[key]) > 1:
shuffle(d[key])
r.extend(d[key])
return r
```

### Exercise 12.3

```import string

def most_frequent(s):
d = dict()
inv = dict()
for char in s:
if char in string.ascii_letters:
letter = char.lower()
d[letter] = d.get(letter, 0) + 1

for letter, freq in d.items():
inv.setdefault(freq, []).append(letter)

for freq in sorted(inv, reverse=True):
print('{:.2%}:'.format(freq/(sum(list(inv)*len(inv[freq])))), ', '.join(inv[freq]))
```

## Chapter 13

### Exercise 13.7

```from string import punctuation, whitespace, digits
from random import randint
from bisect import bisect_left

def process_file(filename):
h = dict()
fp = open(filename)
for line in fp:
process_line(line, h)
return h

def process_line(line, h):
line = line.replace('-', ' ')
for word in line.split():
word = word.strip(punctuation + whitespace + digits)
word = word.lower()
if word != '':
h[word] = h.get(word, 0) + 1

hist = process_file('emma.txt')

def cum_sum(list_of_numbers):
cum_list = []
for i, elem in enumerate(list_of_numbers):
if i == 0:
cum_list.append(elem)
else:
cum_list.append(cum_list[i-1] + elem)
return cum_list

def random_word(h):
word_list = list(h.keys())
num_list = []
for word in word_list:
num_list.append(h[word])
cum_list = cum_sum(num_list)
i = randint(1, cum_list[-1])
pos = bisect_left(cum_list, i)
return word_list[pos]

print(random_word(hist))
```

## Chapter 14

### Exercise 14.3

```import shelve

def dict_of_signatures_and_words(filename='words.txt'):
d = dict()
for line in open(filename):
word = line.lower().strip()
signature = ''.join(sorted(word))
d.setdefault(signature, []).append(word)
return d

def db_of_anagrams(filename='anagrams', d=dict_of_signatures_and_words()):
db = shelve.open(filename)
for key, values in d.items():
if len(values)>1:
for index, value in enumerate(values):
db[value]=values[:index]+values[index+1:]
db.close()

def print_contents_of_db(filename='anagrams'):
db = shelve.open(filename, flag='r')
for key in sorted(db):
print(key.rjust(12), '\t<==>\t', ', '.join(db[key]))
db.close()

db_of_anagrams()
print_contents_of_db()
```

### Exercise 14.5

```# Replace urllib.request with urllib if you use Python 2.
# I would love to see a more elegant solution for this exercise, possibly by someone who understands html.

import urllib.request

def check(zip_code):
if zip_code == 'done':
return False

else:
if len(zip_code) != 5:
print('\nThe zip code must have five digits!')
return True

def get_html(zip_code):
gibberish = urllib.request.urlopen('http://www.uszip.com/zip/' + zip_code)
return less_gib

def extract_truth(code, key, delimiter):
pos = code.find(key) + len(key)
nearly_true = code[pos:pos+40]
truth = nearly_true.split(delimiter)
return truth

while True:
zip_code = input('Please type a zip code (5 digits) or "done" if want to stop:\n')

if not check(zip_code):
break

code = get_html(zip_code)

invalid_key = '(0 results)'
if invalid_key in code:
print('\nNot a valid zip code.')
continue

name_key = '<title>'
name_del = ' zip'
name = extract_truth(code, name_key, name_del)

pop_key = 'Total population</dt><dd>'
pop_del = '<'
pop = extract_truth(code, pop_key, pop_del)

if not 1 < len(pop) < 9:
pop = 'not available'

print('\n' + name)
print('Population:', pop, '\n')
```

## Chapter 15

### Exercise 15.1

```import math

class Point(object):
"""represents a point in 2-D space"""

def distance(p1, p2):
distance = math.sqrt((p2.x - p1.x)**2 + (p2.y - p1.y)**2)
return distance

p1 = Point()
p2 = Point()

p1.x = 3
p1.y = 2
p2.x = 4
p2.y = 3

print(distance(p1, p2))
```

### Exercise 15.3

```import copy

def move_rectangle(rec, dx, dy):
""" does a deep copy and return the newRec with changes applied """
newRec = copy.deepcopy(rec)
newRec.corner.x += dx
newRec.corner.y += dy

return newRec
```

## Chapter 16

### Exercise 16.1

```def print_time(t):
print '%.2d:%.2d:%.2d' % (t.hour, t.minute, t.second)
```

or

```# Solution for Python3
# More on string formatting: http://docs.python.org/py3k/library/string.html#formatspec

def print_time(t):
# 0 is a fill character, 2 defines the width
print('{}:{:02}:{:02}'.format(t.hour, t.minute, t.second))
```

### Exercise 16.2

```def is_after(t1, t2):
return (t1.hour, t1.minute, t1.second) > (t2.hour, t2.minute, t2.second)
```

### Exercise 16.3

```# Comment not by the author: This will give a wrong result, if (time.second + seconds % 60) > 60

def increment(time, seconds):

n = seconds/60
time.second += seconds - 60.0*n
time.minute += n

m = time.minute/60
time.minute -= m*60
time.hour += m
```

or

```# Solution for Python3
# Replace '//' by '/' for Python2

def increment(time, seconds):
time.second += seconds
time.minute += time.second//60
time.hour += time.minute//60

time.second %= 60
time.minute %= 60
time.hour %= 24
```
```# A different way of going about it

def increment(time, seconds):
# Converts total to seconds, then back to a readable format
time.second = time.hour*3600 + time.minute*60 + time.second + seconds
(time.minute, time.second) = divmod(time_in_seconds, 60)
(time.hour, time.minute) = divmod(time.minute, 60)
```

### Exercise 16.4

```# Solution for Python3
# Replace '//' by '/' for Python2

from copy import deepcopy

def increment(time, seconds):
r = deepcopy(time)

r.second += seconds
r.minute += r.second//60
r.hour += r.minute//60

r.second %= 60
r.minute %= 60
r.hour %= 24

return r
```

### Exercise 16.5

```class Time(object):
"""represents the time of day.
attributes: hour, minute, second"""

time = Time()
time.hour = 11
time.minute = 59
time.second = 30

def time_to_int(time):
minutes = time.hour * 60 + time.minute
seconds = minutes * 60 + time.second
return seconds

def int_to_time(seconds):
time = Time()
minutes, time.second = divmod(seconds, 60)
time.hour, time.minute = divmod(minutes, 60)
return time

seconds = time_to_int(time)

def print_time (x):
print 'The time is %.2d : %.2d : %.2d' % (x.hour, x.minute, x.second)
print_time (time)

newtime = increment (time, 70)

print_time (newtime)
```

### Exercise 16.6

```def time_to_int(time):
minutes = time.hour * 60 + time.minute
seconds = minutes * 60 + time.second
return seconds

def int_to_time(seconds):
time = Time()
minutes, time.second = divmod(seconds, 60)
time.hour, time.minute = divmod(minutes, 60)
return time

def mul_time(time, factor):
seconds = time_to_int(time)
seconds *= factor
seconds = int(seconds)
return int_to_time(seconds)

def average_pace(time, distance):
return mul_time(time, 1/distance)
```

### Exercise 16.7

Write a class definition for a Date object that has attributes day, month and year. Write a function called increment_date that takes a Date object, date, and an integer, n, and returns a new Date object that represents the day n days after date. Hint: “Thirty days hath September...” Challenge: does your function deal with leap years correctly? See wikipedia.org/wiki/Leap_year.

```class Date(object):
"""represents a date.
attributes: day, month, year"""

def print_date(date):
# German date format

print('{}.{}.{}'.format(date.day, date.month, date.year))

def is_leap_year(year):
# http://en.wikipedia.org/wiki/Leap_year#Algorithm

if year % 4 == 0:
if year % 100 == 0:
if year % 400 == 0:
return True
return False
return True
return False

def month_list(year):
if is_leap_year(year):
return [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
return [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

def days_of_year(year):
if is_leap_year(year):
return 366
return 365

def date_to_int(date):
days = 0
for year in range(1, date.year):
days += days_of_year(year)

month_days = month_list(date.year)
for month in range(1, date.month):
days += month_days[month - 1]

days += date.day - 1
return days

def int_to_date(days):
date = Date()

date.year = 1
next_days = 365
while days >= next_days:
date.year += 1
days -= next_days
next_days = days_of_year(date.year)

date.month = 1
next_days = 31
month_days = month_list(date.year)
while days >= next_days:
date.month += 1
days -= next_days
next_days = month_days[date.month - 1]

date.day = days + 1
return date

def increment_date(date, n):
days = date_to_int(date)
return int_to_date(days + n)

d1 = Date()
d1.day, d1.month, d1.year = 8, 3, 2012
print_date(d1)

d2 = increment_date(d1, 7)
print_date(d2)
```

### Exercise 16.8

1. Use the datetime module to write a program that gets the current date and prints the day of the week.

```from datetime import date

def current_weekday():
i = date.today()
print i.strftime('%A')

current_weekday()
```

2. Write a program that takes a birthday as input and prints the user’s age and the number of days, hours, minutes and seconds until their next birthday.

```# Python3 solution. Replace "input" by "raw_input" for Python2.
from datetime import datetime

def time_until_birthday():
'the format "mm/dd/yyyy": '))
dob = datetime.strptime(dob_input, '%m/%d/%Y')
now = datetime.now()
if now > datetime(now.year, dob.month, dob.day):
age = now.year - dob.year
next_year = True
else:
age = now.year - dob.year - 1
next_year = False
time_to_birthday = datetime(now.year + next_year,
dob.month, dob.day) - now
days = time_to_birthday.days
hours, remainder = divmod(time_to_birthday.seconds, 3600)
minutes, seconds = divmod(remainder, 60)
print("\nYou are {} years old.".format(age))
print(("You have {0} days, {1} hours, {2} minutes and {3} "
"seconds left until your next birthday.").format(
days, hours, minutes, seconds))

time_until_birthday()
```

## Chapter 17

### Exercise 17.8

2.

```from visual import scene, sphere

scene.range = (256, 256, 256)
scene.center = (128, 128, 128)

t = range(0, 256, 51)

for x in t:
for y in t:
for z in t:
pos = x, y, z
color = (x/255., y/255., z/255.)
```

3. Download http://thinkpython.com/code/color_list.py and use the function read_colors to generate a list of the available colors on your system, their names and RGB values. For each named color draw a sphere in the position that corresponds to its RGB values.

```# As there currently (2013-04-12) is no function read_colors in color_list.py
# I use a workaround and simply import the variable COLORS from color_list.py.
# I then use the function all_colors() on COLORS to get a list of the colors.

from color_list import COLORS
from visual import scene, sphere

def all_colors(colors_string=COLORS):
"""Extract a list of unique RGB-tuples from COLORS.
The tuples look like (r, g, b), where r, g and b are each integers in
[0, 255].
"""

# split the string into lines and remove irrelevant lines
lines = colors_string.split('\n')[2:-2]

# split the individual lines and remove the names
numbers_only = [line.split()[:3] for line in lines]

# turn strings into ints and rgb-lists into tuples
rgb_tuples = [tuple([int(s) for s in lst]) for lst in numbers_only]

# return a list of unique tuples
return list(set(rgb_tuples))

def make_spheres(color_tuples=all_colors()):
scene.range = (256, 256, 256)
scene.center = (128, 128, 128)
for (r, g, b) in color_tuples:
sphere(pos=(r, g, b), radius=7, color=(r/255., g/255., b/255.))

if __name__ == '__main__':
make_spheres()
```

## Chapter 3.5

### calculator

```#recursion or recursive
print "\n	INDEX\n""\n	C=1 for addition\n""\n	C=2 for substraction\n""\n
C=3 for multiplication\n""\n	C=4 for division\n""\n	C=5 for to find modulus\n""\n	C=6 to find factorial\n"
c=x+y
print x,"+",y,"=",c
def sub(x,y):
c=x-y
print x,"-",y,"=",c
def mul(x,y):
c=x*y
print x,"*",y,"=",c
def div(x,y):
c=x/y
print x,"/",y,"=",c
def mod(x,y):
c=x%y
print x,"%",y,"=",c
if C==6:
def f(n):
if n==1:
print n
return n
else:
print n,"*",
return n*f(n-1)
print f(n)
if C==1:
a=input("Enter your first no here: ")
b=input("Enter your second no here: ")
elif C==2:
a=input("Enter your first no here: ")
b=input("Enter your second no here: ")
sub(a,b)
elif C==3:
a=input("Enter your first no here: ")
b=input("Enter your second no here: ")
mul(a,b)
elif C==4:
a=input("Enter your first no here: ")
b=input("Enter your second no here: ")
div(a,b)
elif C==5:
a=input("Enter your first no here: ")
b=input("Enter your second no here: ")
mod(a,b)
```

### palindrome

```def first(word):
return word
def last(word):return word[-1]
def middle(word):
return word[1:-1]
def palindrome(word):
if first(word)==last(word):
word = middle(word)
n=len(word)
if n<2:
print "palindrome"
else:
return palindrome(word)
else:
print "not palindrome"

word=raw_input("Enter the  string:")
palindrome(word)
```

### sum of all digits

```def sum_of_n_numbers(number):
if(number==0):
return 0
else:
return number + sum_of_n_numbers(number-1)
num = raw_input("Enter a number:")
num=int(num)
sum = sum_of_n_numbers(num)
print sum
###another answer in case of while loops
def sum_of_Digits(number):
sum=0
while number>0:
digit=number%10
sum=sum+digit
number=number/10
return sum
num=raw_input("enter the number")
num=int(num)
sum_of_digits=sum_of_Digits(num)
print sum_of_digits
```

### Exercise 18.5

```class Card(object):

suit_names = ['Clubs', 'Diamonds', 'Hearts', 'Spades']
rank_names = [None, 'Ace', '2', '3', '4', '5', '6', '7',
'8', '9', '10', 'Jack', 'Queen', 'King']

def __init__(self, suit = 0, rank = 2):
self.suit = suit
self.rank = rank

def __str__(self):
return '%s of %s' % (Card.rank_names[self.rank],
Card.suit_names[self.suit])

def __cmp__(self, other):
c1 = (self.suit, self.rank)
c2 = (other.suit, other.rank)
return cmp(c1, c2)

def is_valid(self):
return self.rank > 0

class Deck(object):

def __init__(self, label = 'Deck'):
self.label = label
self.cards = []
for i in range(4):
for k in range(1, 14):
card = Card(i, k)
self.cards.append(card)

def __str__(self):
res = []
for card in self.cards:
res.append(str(card))
print self.label
return '\n'.join(res)

def deal_card(self):
return self.cards.pop(0)

self.cards.append(card)

def shuffle(self):
import random
random.shuffle(self.cards)

def sort(self):
self.cards.sort()

def move_cards(self, other, num):
for i in range(num):

def deal_hands(self, num_hands, num_cards):
if num_hands*num_cards > 52:
return 'Not enough cards.'

l = []

for i in range(1, num_hands + 1):
hand_i = Hand('Hand %d' % i)
self.move_cards(hand_i, num_cards)
l.append(hand_i)

return l

class Hand(Deck):

def __init__(self, label = ''):
self.cards = []
self.label = label

# 18-6, 1-4:
class PokerHand(Hand):

def suit_hist(self):
self.suits = {}
for card in self.cards:
self.suits[card.suit] = self.suits.get(card.suit, 0) + 1
return self.suits

def rank_hist(self):
self.ranks = {}
for card in self.cards:
self.ranks[card.rank] = self.ranks.get(card.rank, 0) + 1
return self.ranks

def P(self):
self.rank_hist()
for val in self.ranks.values():
if val >= 2:
return True
return False

def TP(self):
self.rank_hist()
count = 0
for val in self.ranks.values():
if val == 4:
return True
elif val >= 2 and val < 4:
count += 1
return count >= 2

def TOAK(self):
self.rank_hist()
for val in self.ranks.values():
if val >= 3:
return True
return False

def STRseq(self):
seq = []
l = STRlist()
self.rank_hist()
h = self.ranks.keys()
h.sort()
if len(h) < 5:
return []

# Accounts for high Aces:
if 1 in h:
h.append(1)

for i in range(5, len(h)+1):
if h[i-5:i] in l:
seq.append(h[i-5:i])
return seq

def STR(self):
seq = self.STRseq()
return seq != []

def FL(self):
self.suit_hist()
for val in self.suits.values():
if val >= 5:
return True
return False

def FH(self):
d = self.rank_hist()
keys = d.keys()

for key in keys:
if d[key] >= 3:
keys.remove(key)
for key in keys:
if d[key] >= 2:
return True
return False

def FOAK(self):
self.rank_hist()
for val in self.ranks.values():
if val >= 4:
return True
return False

def SFL(self):
seq = self.STRseq()
if seq == []:
return False
for list in seq:
list_suits = []
for index in list:
for card in self.cards:
if card.rank == index:
list_suits.append(card.suit)
list_hist = histogram(list_suits)
for key in list_hist.keys():
if list_hist[key] >= 5:
return True
return False

def classify(self):
self.scores = []
hands = ['Pair', 'Two-Pair',
'Three of a Kind', 'Straight',
'Flush', 'Full House',
'Four of a Kind', 'Straight Flush']
if self.P():
self.scores.append(1)
if self.TP():
self.scores.append(2)
if self.TOAK():
self.scores.append(3)
if self.STR():
self.scores.append(4)
if self.FL():
self.scores.append(5)
if self.FH():
self.scores.append(6)
if self.FOAK():
self.scores.append(7)
if self.SFL():
self.scores.append(8)
if self.scores != []:
return hands[max(self.scores)-1]

def STRlist():
s = []
for i in range(0,9):
s.append(range(1,14)[i:i+5])
s.append([10,11,12,13,1])
return s

def histogram(l):
d = dict()
for k in range(len(l)):
d[l[k]] = 1 + d.get(l[k],0)
return d

# 18-6, 5:
def p(config = '', trials = 10000, n = 1):
"""Estimates probability that the
nth dealt hand will be config. A hand
consists of seven cards."""

successes = 0

for i in range(1, trials + 1):
deck = Deck('Deck %d' % i)
deck.shuffle()

box = Hand()
deck.move_cards(box, (n-1)*7)

hand = PokerHand('Poker Hand %d' % i)
deck.move_cards(hand, 7)
if hand.classify() == config:
successes += 1

return 1.0*successes/trials

#Iterate until first desired config.:
if __name__ == '__main__':

c = 1

while True:
deck = Deck()
deck.shuffle()
hand = PokerHand('Poker Hand %d' % c)
deck.move_cards(hand, 5)
print hand
print hand.SFL()
if hand.SFL():
print hand.STRseq()
break
print ''
c += 1

Code by Victor Alvarez
```

## Appendix B

### Exercise B.3

Write a function called bisection that takes a sorted list and a target value and returns the index of the value in the list, if it’s there, or None if it’s not.

```from bisect import bisect_left

def bisection(sorted_list, item):
i = bisect_left(sorted_list, item)
if i < len(sorted_list) and sorted_list[i] == item:
return i
else:
return None

if __name__ == '__main__':
a = [1, 2, 3]
print(bisection(a, 2))  # expect 1
b = [1, 3]
print(bisection(b, 2))  # expect None
c = [1, 2]
print(bisection(c, 3))  # expect None
```