Percent in python’s string formatting

In python, we don’t need to escape the char ‘%’ in a string, except when we want to format the specific string. Examples:

>>> 'Here is a percent: %'
'Here is a percent: %'

>>> 'Here is two percent %%'
'Here is two percent %%'

>>> 'Here is a percent %% %s' % 'in formatted string'
'Here is a percent % in formatted string'

>>> 'We have to double the percent % %s!' % 'in formatted string'
Traceback (most recent call last):
  File "", line 1, in 
TypeError: not all arguments converted during string formatting

>>> 'If we do not specify a format, we must not double the percent: %(foo)s %(bar)s!'
'If we do not specify a format, we must not double the percent: %(foo)s %(bar)s!'

>>> 'If we want to format specifically, we must double the percent: %(foo)s %%(bar)s!' % {'foo': 'test'}
'If we want to format specifically, we must double the percent: test %(bar)s!'

>>> 'And of course this will crash: %(foo)s %(bar)s!' % {'foo': 'test'}
Traceback (most recent call last):
  File "", line 1, in 
KeyError: 'bar'