string formatting in Python

Qianjiang Hu
2022-04-16

name = 'QJ'
age = 16

% Operator

%d will truncate to integer, %s will maintain formatting, %f will print as float and %g is used for generic number %x format specifier convert an int value to a string and represent it as a hexadecimal number

'Hello, this is %s; I am %d years old' %(name, age)

'Hello, this is QJ; I am 16 years old'

name ='QJ'
number = 16.6
print('QJ is printing: %s (str) %s (str) %d (integer) %f (float) %g (generic number)' % (name, number, number, number, number))

QJ is printing: QJ (str) 16.6 (str) 16 (integer) 16.600000 (float) 16.6 (generic number)

It’s also possible to refer to variable substitutions by name if passing a mapping to the % operator

'Hey, this is %(name)s; I am %(age)d years old!' % {"name": name, "age": age}

'Hey, this is QJ; I am 16 years old!'

'{}'.format()

name = 'QJ'
age = 16
'Hey, {name}, are you {age} years old？'.format(name=name, age = age)

'Hey, QJ, are you 16 years old？'

f-Strings

f'{}'

f'Hey, {name}, are you {age} years old？'

'Hey, QJ, are you 16 years old？'

a = 5
b = 10

f'Five plus ten is {a + b} and not {2 * (a + b)}.'

'Five plus ten is 15 and not 30.'

def selfintro(name, age):
     return f"Hello, {name} is {age} years old?"

selfintro('QJ', '16')

'Hello, QJ is 16 years old?'

Template Strings (Standard Library)

from string import Template

t = Template('Hey, $name!')
t.substitute(name=name)

'Hey, QJ!'

sample = 'Hey $name, I am $age years old!'
Template(sample).substitute(name=name, age = age)

'Hey QJ, I am 16 years old!'