print "abc" + 123
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: cannot concatenate 'str' and 'int' objects

print '%s+%d' % ('abc', 123) #abc+123
print '%o' % 10 #12 八进制

print '%s+%05d' % ('abc', 123) #abc+00123
print '%03x' % 10 #00a
print '%.3e' % 123456789 #1.235e+08 保留3位小数的科学技术法

print '{0}{1}{2}{3}'.format('a', 'b', 'c', 123) #abc123
print '{}, {}, {}'.format('a', 'b', 'c') #abc 2.7+ only
print '{2}, {1}, {0}'.format('a', 'b', 'c') #c, b, a
print '{2}, {1}, {0}'.format(*'abc') #c, b, a
print '{0}{1}{0}'.format('abra', 'cad') #abracadabra

print 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W') #Coordinates: 37.24N, -115.81W
coord = {'latitude': '37.24N', 'longitude': '-115.81W'}
print 'Coordinates: {latitude}, {longitude}'.format(**coord) #Coordinates: 37.24N, -115.81W

coord = (3, 5)
print 'X: {0[0]}; Y: {0[1]}'.format(coord) #X: 3; Y: 5

# format also supports binary numbers
"int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}".format(42) #'int: 42; hex: 2a; oct: 52; bin: 101010'
3 
# with 0x, 0o, or 0b as prefix:
"int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}".format(42) #'int: 42; hex: 0x2a; oct: 0o52; bin: 0b101010'

'{:,}'.format(1234567890) #'1,234,567,890'

'{:.2%}'.format(19.5 / 22) # '88.64%'

import datetime
today = datetime.datetime.today()
'{:%Y-%m-%d %H:%M:%S}'.format(d) #'2013-09-01 21:10:22'
'{:%Y-%m-%d}'.format(today) #'2013-09-01'

from string import Template
s = Template('$sargs plus $aargs')
s.substitute(sargs = 'abc', aargs = 123) #'abc plus 123'

d = dict(sargs = 'abc')
# s.substitute(d)
# it's a KeyError
s.safe_substitute(d) #'abc plus $aargs'