Code for chapter 18

# Script 18.1
mass = 3.4
volume = 1.8
density = mass/volume       # Division
density = round(density, 3) # Round to three decimal places
print(density)

[ah@hobbes Documents]$ python script_18_1.py 
1.889
[ah@hobbes Documents]$

# Script 18.2
x = 2     # Integer
y = 5     # Integer
z = 3.0   # Floating point

print(x * y) # 10  - Integer
print(x / y) # 0.4 - Floating point due to division
print(x + z) # 5.0 - Floating point

t = type(x * y - z)  # Get a value's data type
print(t)             # float

[ah@hobbes Documents]$ python script_18_2.py 
10
0
5.0
<type 'float'>
[ah@hobbes Documents]$

# Script 18.3
x = 1            # An arbitrary integer
print(x.__doc__) # Print Python documentation for this object

[ah@hobbes Documents]$ python script_18_3.py 
int(x=0) -> int or long
int(x, base=10) -> int or long

Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is floating point, the conversion truncates towards zero.
If x is outside the integer range, the function returns a long instead.

If x is not a number or if base is given, then x must be a string or
Unicode object representing an integer literal in the given base.  The
literal can be preceded by '+' or '-' and be surrounded by whitespace.
The base defaults to 10.  Valid bases are 0 and 2-36.  Base 0 means to
interpret the base from the string as an integer literal.
>>> int('0b100', base=0)
4
[ah@hobbes Documents]$ 

# Script 18.4
x = True
print(x)
print(bool(0.0)) # False
print(bool(7))   # True

[ah@hobbes Documents]$ python script_18_4.py 
True
False
True
[ah@hobbes Documents]$

# Script 18.5
x = 2
print(x > 5) # False
y = x < 3
print(y)     # True

[ah@hobbes Documents]$ python script_18_5.py 
False
True
[ah@hobbes Documents]$ 

# Script 18.6
x = 1
y = -1
x > y and y > 1   # False - second comparison is False
print(x > y and y > 1)
x != 2 or y == 1  # True - first comparison is True; x does not equal 2
print(x != 2 or y == 1)
not (y > x)       # True - comparison is False; not False is True
print(not (y > x))

[ah@hobbes Documents]$ python script_18_6.py 
False
True
True
[ah@hobbes Documents]$ 

# Script 18.7
x = 'Hello'
y = "world"
print(x,y)  # Print both values to screen

[ah@hobbes Documents]$ python script_18_7.py 
('Hello', 'world')
[ah@hobbes Documents]$ 

# Script 18.8
x = '''This text flows from one line
to the next line inside triple quotes'''
print(x)

[ah@hobbes Documents]$ python script_18_8.py 
This text flows from one line
to the next line inside triple quotes
[ah@hobbes Documents]$ 

# Script 18.9
x = 'abcde'
print(len(x)) # 5 
print(x[0])   # First character 'a' at index 0
print(x[-1])  # Last character 'e'
print(x[1:3]) # 'bcd' range from index 1, up to, but not including 3

[ah@hobbes Documents]$ python script_18_9.py 
5
a
e
bc
[ah@hobbes Documents]$ 

# Script 18.10
name = 'Mary'
x = 0.12
y = 34121.0

a = 'Hello {}'.format(name)    # name replaces brackets
print(a)                       # 'Hello Mary'

b = 'X {:.5f} Y {:.2e}'.format(x, y)   # 5 dp float 2 dp sci
print(b)                               # 'X 0.12000 Y 3.41e4'
 
c = '{:3d},{:3d}'.format(12,7)   # pad digits to 3 characters
print(c)                         # ' 12,  7'

[ah@hobbes Documents]$ python script_18_10.py 
Hello Mary
X 0.12000 Y 3.41e+04
 12,  7
[ah@hobbes Documents]$ 

# Script 18.11
x = ['a', 'b', 'c', 'd'] 
print(x[2])   # 'c' - the character at index 2
print(x[1:])  # ['b', 'c', 'd'] - from index 1 to the end
x[0] = 'z'    # character at index 0 is set to 'z'
del x[2]      # Deletes item at index 2
print(x)      # ['z', 'b', 'd']

y = [[4,7], [9,6]] # A list containing two other lists
print(y[1])        # [9,6] - the sub-list at y index 1
print(y[1][0])     # 9 - item 0 from sub-list 1  

[ah@hobbes Documents]$ python script_18_11.py 
c
['b', 'c', 'd']
['z', 'b', 'd']
[9, 6]
9
[ah@hobbes Documents]$ 

# Script 18.12
x = list('PQRST')     # Create list from text string
print(x)              # ['P','Q','R','S','T'] - list of characters
y = list(range(10))   # A list of the range from 0 up to <10 
print(y)              # [0,1,2,3,4,5,6,7,8,9]

[ah@hobbes Documents]$ python script_18_12.py 
['P', 'Q', 'R', 'S', 'T']
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[ah@hobbes Documents]$ 

# Script 18.13
x = [4, 1, 0] # Three items 
a, b, c = x   # a is 4, b is 1, c is 0
x = ['a', 'b', 'c', 'd']
print(len(x))     # 4 - number of items in list
print('c' in x)   # True - string 'c' is in the list
print(2 in x)     # False - number 2 is not in list

[ah@hobbes Documents]$ python script_18_13.py 
4
True
False
[ah@hobbes Documents]$ 

# Script 18.14
x = (9, 3, 1, 0)  # Create a tuple
y = (2,)          # Tuple with one item (needs trailing comma)
z = ()            # Empty tuple

print(x[-1])      # Print the last item - 0
#x[0] = 6          # Does not work! Tuples cannot be changed!

w = list(x)       # Create equivalent list from a tuple
w[0] = 6          # List copy can be changed 
print('x',x)
print('w',w)

[ah@hobbes Documents]$ python script_18_14.py 
0
('x', (9, 3, 1, 0))
('w', [6, 3, 1, 0])
[ah@hobbes Documents]$ 

# Script 18.15
x = {1,2,3,4,3,2,1}  # x is {1,2,3,4} - duplicates ignored
y = set([3,4,5,6])   # y created from a list
print(len(y))        # 4
print(1 in y)        # False; 1 is not in y
print(x & y)         # {3,4} - intersection, items in both
print(x | y)         # {1,2,3,4,5,6} - union, items in either

[ah@hobbes Documents]$ python script_18_15.py 
4
False
set([3, 4])
set([1, 2, 3, 4, 5, 6])
[ah@hobbes Documents]$ 

# Script 18.16
d = {"G":329.21, "C":289.18, "A":313.21, "T":314.19}
print(d['A'])      # 313.21 -  value associated with 'A'
print(len(d))      # 4 - number of key:value pairs
print(d.keys())    # Just keys 'G', 'A', 'T', 'C'
print(d.values())  # Just values 329.21, 313.21, 314.19, 289.18

[ah@hobbes Documents]$ python script_18_16.py 
313.21
4
['A', 'C', 'T', 'G']
[313.21, 289.18, 314.19, 329.21]
[ah@hobbes Documents]$ 

# Script 18.17
d = {"G":329.21, "C":289.18, "A":313.21, "T":314.19}
d['T'] = 304.19   # Change the value of an existing item
d['U'] = 291.08   # Add a new key:value pair
print(len(d))     # 5 - dict is larger  
del d['U']        # Delete a key and its value from the dictionary

[ah@hobbes Documents]$ python script_18_17.py 
5
[ah@hobbes Documents]$ 

# Script 18.18
x = ['Mon', 'Tue', 'Wed'] # A list of strings
y = ['Fri', 'Sat', 'Sun'] # And another
x.append('Thu')  # Add a single new item to end
print(x)
x.extend(y)       # Extend with items from another collection 
print(x)
x.sort()         # Sort contents alphabetically
print(x)
x.remove('Sun')  # Remove an item
print(x)
x.index('Sat')   # Positional index of an item
print(x)

[ah@hobbes Documents]$ python script_18_18.py 
['Mon', 'Tue', 'Wed', 'Thu']
['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
['Fri', 'Mon', 'Sat', 'Sun', 'Thu', 'Tue', 'Wed']
['Fri', 'Mon', 'Sat', 'Thu', 'Tue', 'Wed']
['Fri', 'Mon', 'Sat', 'Thu', 'Tue', 'Wed']
[ah@hobbes Documents]$ 

# Script 18.19
s = {'G', 'C', 'A', 'T'}   # A set with 4 strings
t = {'N', 'R', 'Y'}
print(s)
s.add('U')       # Add a single item (if not present) 
print(s)
s.update(t)      # Add any new items from another collection
print(s)

[ah@hobbes Documents]$ python script_18_19.py 
set(['A', 'C', 'T', 'G'])
set(['A', 'C', 'U', 'T', 'G'])
set(['A', 'C', 'G', 'N', 'R', 'U', 'T', 'Y'])
[ah@hobbes Documents]$