Python 2.7 quick reference

Python versions before 2.6 did not have the string .format() method described in Section 9.4, “The string .format() method”. Instead, string formatting used this general form:

f % v

where f is a template string and v specifies the value or values to be formatted using that template. If multiple values are to be formatted, v must be a tuple.

The template string may contain any mixture of ordinary text and format codes. A format code always starts with a percent (%) symbol. See Table 4, “Format codes”.

The result of a format operation consists of the ordinary characters from the template with values substituted within them wherever a format code occurs. A conversational example:

>>> print "We have %d pallets of %s today." % (49, "kiwis")
We have 49 pallets of kiwis today.

In the above example, there are two format codes. Code “%d” means “substitute a decimal number here,” and code “%s” means “substitute a string value here”. The number 49 is substituted for the first format code, and the string "kiwis" replaces the second format code.

In general, format codes have this form:

%[p][m[.n]]c

Here are the format type codes, c in the general expression above:

>>> '%4o' % 127
' 177'
>>> '%#4o' % 127
'0177'
>>> '%x' % 127
'7f'
>>> '%#x' % 127
'0x7f'
>>> '%10.5g' % 0.5
'       0.5'
>>> '%#10.5g' % 0.5
'   0.50000'

You can also use the string format operator % to format a set of values from a dictionary D (see Section 16, “Type dict: Dictionaries”):

f % D

In this form, the general form for a format code is:

%(k)[p][m[.n]]c

where k is a key in dictionary D, and the rest of the format code is as in the usual string format operator. For each format code, the value of D[k] is used. Example:

>>> named = {'last': 'Poe', 'first': 'Aloysius'}
>>> 'Dear %(first)s %(last)s:' % named
'Dear Aloysius Poe:'