第七章 String 基础

1.String Basics

>>> title = "Meaning " 'of' " Life" # Implicit concatenation
>>> title
'Meaning of Life'

>>> s = 'a\0b\0c'
>>> s
'a\x00b\x00c'


myfile = open(r'C:\new\text.dat', 'w')
myfile = open('C:\\new\\text.dat', 'w')

>>> path = r'C:\new\text.dat'
>>> path # Show as Python code
'C:\\new\\text.dat'
>>> print(path) # User-friendly format
C:\new\text.dat
 

2.Strings in Action

% python
>>> len('abc') # Length: number of items
3
>>> 'abc' + 'def' # Concatenation: a new string
'abcdef'
>>> 'Ni!' * 4 # Repetition: like "Ni!" + "Ni!" + ...
'Ni!Ni!Ni!Ni!'

>>> myjob = "hacker"
>>> for c in myjob: print(c, end=' ') # Step through items, print each (3.X form)
...
h a c k e r
>>> "k" in myjob # Found
True
>>> "z" in myjob # Not found
False
>>> 'spam' in 'abcspamdef' # Substring search, no position returned
True

>>> S = 'spam'
>>> S[0], S[−2] # Indexing from front or end
('s', 'a')
>>> S[1:3], S[1:], S[:−1] # Slicing: extract a section
('pa', 'pam', 'spa')


>>> S = 'abcdefghijklmnop'
>>> S[1:10:2] # Skipping items
'bdfhj'
>>> S[::2]
'acegikmo'

>>> S = 'hello'
>>> S[::−1] # Reversing items
'olleh'


>>> 'spam'[1:3] # Slicing syntax
'pa'
>>> 'spam'[slice(1, 3)] # Slice objects with index syntax + object
'pa'
>>> 'spam'[::-1]
'maps'
>>> 'spam'[slice(None, None, −1)]
'maps'

>>> int("42"), str(42) # Convert from/to string
(42, '42')
>>> repr(42) # Convert to as-code string
'42'
>>> print(str('spam'), repr('spam')) # 2.X: print str('spam'), repr('spam')
spam 'spam'
>>> str('spam'), repr('spam') # Raw interactive echo displays
('spam', "'spam'")

>>> ord('s')
115
>>> chr(115)
's'


>>> int('1101', 2) # Convert binary to integer: built-in
13
>>> bin(13) # Convert integer to binary: built-in
'0b1101'

>>> 'That is %d %s bird!' % (1, 'dead') # Format expression: all Pythons
That is 1 dead bird!
>>> 'That is {0} {1} bird!'.format(1, 'dead') # Format method in 2.6, 2.7, 3.X
'That is 1 dead bird!'

>>> '%s -- %s -- %s' % (42, 3.14159, [1, 2, 3]) # All types match a %s target
'42 -- 3.14159 -- [1, 2, 3]'



>>> 'My %(kind)s runs %(platform)s' % {'kind': 'laptop', 'platform': sys.platform}
'My laptop runs win32'

%[(keyname)][flags][width][.precision]typecode

>>> x = 1234
>>> res = 'integers: ...%d...%−6d...%06d' % (x, x, x)
>>> res
'integers: ...1234...1234 ...001234'


>>> x = 1.23456789
>>> x # Shows more digits before 2.7 and 3.1
1.23456789
>>> '%e | %f | %g' % (x, x, x)
'1.234568e+00 | 1.234568 | 1.23457'
>>> '%E' % x
'1.234568E+00'

>>> '%-6.2f | %05.2f | %+06.1f' % (x,x,x)
'1.23   | 01.23 | +001.2'

>>> '%f, %.2f, %.*f' % (1/3.0, 1/3.0, 4, 1/3.0)
'0.333333, 0.33, 0.3333'

>>> '%(qty)d more %(food)s' % {'qty': 1, 'food': 'spam'}
'1 more spam'

>>> template = '{0}, {1} and {2}' # By position
>>> template.format('spam', 'ham', 'eggs')
'spam, ham and eggs'
>>> template = '{motto}, {pork} and {food}' # By keyword
>>> template.format(motto='spam', pork='ham', food='eggs')
'spam, ham and eggs'
>>> template = '{motto}, {0} and {food}' # By both
>>> template.format('ham', motto='spam', food='eggs')
'spam, ham and eggs'
>>> template = '{}, {} and {}' # By relative position
>>> template.format('spam', 'ham', 'eggs') # New in 3.1 and 2.7
'spam, ham and eggs

>>> import sys
>>> 'My {1[kind]} runs {0.platform}'.format(sys, {'kind': 'laptop'})
'My laptop runs win32'

>>> 'My {map[kind]} runs {sys.platform}'.format(sys=sys, map={'kind': 'laptop'})
'My laptop runs win32'

{fieldname component !conversionflag :formatspec}

formatspec：

[[fill]align][sign][#][0][width][,][.precision][typecode]

>>> '{0:10} = {1:10}'.format('spam', 123.4567) # In Python 3.3
'spam = 123.4567'
>>> '{0:>10} = {1:<10}'.format('spam', 123.4567)
' spam = 123.4567 '
>>> '{0.platform:>10} = {1[kind]:<10}'.format(sys, dict(kind='laptop'))
' win32 = laptop
>>> '{.platform:>10} = {[kind]:<10}'.format(sys, dict(kind='laptop'))
' win32 = laptop '

>>> '{0:.{1}f}'.format(1 / 3.0, 4) # Take value from arguments
'0.3333'
>>> '%.*f' % (4, 1 / 3.0) # Ditto for expression
'0.3333'

>>> '{0:b}'.format((2 ** 16) − 1) # Expression (only) binary format code
'1111111111111111'
>>> '%b' % ((2 ** 16) − 1)
ValueError: unsupported format character 'b'...


>>> '%s' % bin((2 ** 16) - 1)[2:] # Slice off 0b to get exact equivalent
'1111111111111111'



>>> '{:,d}'.format(999999999999) # New str.format method feature in 3.1/2.7
'999,999,999,999'
>>> '%s' % commas(999999999999) # But % is same with simple 8-line function
'999,999,999,999'