Python - String Format Method: Adding Keys, Attributes, and Offsets

Introduction

format method calls can support more advanced usage.

The following examples indexes a dictionary on the key "test" and then fetches the attribute "platform" from the already imported sys module object.

The second does the same, but names the objects by keyword instead of position:

Demo

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

Result

Square brackets in format strings can name list offsets to perform indexing.

To name negative offsets or slices, or to use arbitrary expression results in general, you must run expressions outside the format string itself:

Demo

somelist = list('TEST') 
print( somelist )
print( 'first={0[0]}, third={0[2]}'.format(somelist) )

print( 'first={0}, last={1}'.format(somelist[0], somelist[-1]) )   # [-1] fails in fmt 
#   ww w . j  a  v  a2s .  co m
parts = somelist[0], somelist[-1], somelist[1:3]           # [1:3] fails in fmt 
print( 'first={0}, last={1}, middle={2}'.format(*parts) )          # Or '{}' in 2.7/3.1+

Result

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