introduction-1/step-5-strings-formatting.py at master · pythonnortheast/introduction-1 · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
# Everything after the hash symbol is a comment
# Comments continue until the end of the line

# The % (modulo) is the string formatting, or interpolation operator.
# It takes the form >>> format % values
'%s' % 'Hello World'
message = 'The message "%s" is inserted here' % 'What\'s up?'
print message

# The %s format argument converts values to strings...
# As though it were called by str()
'%s' % 42
'%s' % True

class Actor(object):
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return self.name

actor = Actor('John Cleese')
actor
'The actor %s, is tall.' % actor
print actor

# Multiple values are contained in tuples
'%s %s %s %s' % (message, 1939, False, actor)

# All arguments must be used
'%s %s' % (message, 1939, False, actor)

# Values can be contained in a single mapping object (e.g. a dict)
values = {
    'message': message,
    'year': 1939,
    'working': False,
    'name': actor
    }

# And then referenced by name
'%(message)s %(year)s %(working)s %(name)s' % values

# Not all of these named arguments have to be used
'%(message)s' % values
'There is no formatting here' % values

# The %r format argument is used to return an object's representation...
# As though it were called by repr()
'%r' % actor
'The actor %s looks like %r' % (actor, actor)
'The actor %(name)s looks like %(name)r' % {'name': actor}

class Actor(object):
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return self.name
    def __repr__(self):
        return '<Actor(%r)>' % self.name

actor = Actor('John Cleese')
'%r' % actor

# There are other formatting arguments, these are two common ones:
# %d an integer
'%d' % 15.59
# %f represents a float
'%f' % 15.59
'%(balance)f' % {'balance': 15.59}
from math import pi
'%f' % pi

# Minimum width
'%20f' % pi
# Padding (zero fill)
'%020f' % pi
# Conversion
'%+f' % pi
'%+f' % (pi * -1)
# Precision
'%.10f' % pi
'%+020.10f' % pi

# The % operator will eventually be depreceated in favour of
# "new style" formatting via the str.format method using {}
# http://docs.python.org/2/library/string.html#formatspec
'{}'.format('New Style')

# Value arguments can be referenced by order
'{} {} {} {}'.format(message, 1939, False, actor)

# Value arguments can be referenced by position
'{3} {0} {2} {1}'.format(message, 1939, False, actor)

# But not both together
'{3} {} {} {1}'.format(message, 1939, False, actor)

# Values arguments can be referenced by name
'{name} is the name of the actor'.format(name=actor)

# Or both (all unnamed arguments must come before named)
'{name} {} {} {}'.format(message, 1939, False, name=actor)
'{name} {2} {1} {0}'.format(message, 1939, False, name=actor)

# Not all argument values have to be referenced in the format string
'{} {}'.format(message, 1939, False, name=actor)
'{2} {1}'.format(message, 1939, False, name=actor)
'{name}'.format(message, 1939, False, name=actor)

# And argument values can be referenced more than once
'{name} {1} {1} {1}'.format(message, 1939, False, name=actor)

# Attributes of objects can also be accessed
from datetime import date
actor.dob = date(1939, 10, 27)
'{0.name} was born on {0.dob}'.format(actor)
'{actor.name} was born on {actor.dob}'.format(actor=actor)
'{actor.name} was born in {actor.dob.year}'.format(actor=actor)

# List-type arguments expose their items
numbers = [2,4,6,8]
letters = ['a','b','c']
'{0[3]} {1[2]} {0[1]} {1[0]}'.format(numbers, letters)

# Parameters to the format method can be expanded
'{2} {1} {0}'.format(*letters) # Unnamed arguments
'{year}'.format(**values) # Named arguments
'{} {} {} {} {year}'.format('Arg0', 'Arg1', *letters, **values)

# An object's representation value is accessed by !r
'{!r}'.format(actor)
# (!s is also available, but not necessary as it's implied)
'{!s}'.format(actor)
'{}'.format(actor)

# Various formatting options passed after a colon: width, fill, alignment
'{:30}'.format('a small string')
'{:>30}'.format('a small string')
'{:<30}'.format('a small string')
'{:^30}'.format('a small string')
'{:=^30}'.format('a small string')
'{0.name:=^30}'.format(actor)

# Numeric formatting: precision, width, fill, alignment
'{:f}'.format(pi)
'{:.3f}'.format(pi)
'{:15.3f}'.format(pi)
'{:015.3f}'.format(pi)
'{:<015.3f}'.format(pi)

# Types can define their own custom formatters. Notably dates.
'{actor} was born on {actor.dob:%A %d %B, %Y}'.format(actor=actor)

# Using the comma as a thousands separator.
'{:,}'.format(1234567890)

# Expressing a percentage
'{:.2%}'.format(15.5/80)

# http://docs.python.org/2/library/string.html#format-specification-mini-language