String Formatting¶
Using Quotes:
Double Quotes (“): strings that are used for interpolation and/or are that intended for the end-user to see
Single Quotes (‘): everything else
F-Strings¶
PEP 498 - Literal String Interpolation; new in 3.6.
Warning
If your format strings are user-supplied, use Template Strings to avoid security issues.
name = "Eric"
age = 74
f"Hello, {name}, You are {age}"
'Hello, Eric. You are 74.'
f"{name = }" # Spaces are preserved
"name = 'Eric'"
# Arbitrary Expressions
f"{2 * 37}
'74'
# Call functions
def to_lowercase(input):
return input.lower()
name = "Eric Idle"
f"{to_lowercase(name)} is funny."
'eric idle is funny.'
f"{name.lower()} is funny."
'eric idle is funny.'
# Datetime
now = datetime.datetime.utcnow()
f'{now = :%Y-%m-%d}'
'now = 2022-04-21'
# Multiline f-Strings
message = f"Hi {name}. " \
f"You are a {profession}. " \
f"You were in {affiliation}."
'Hi Eric. You are a comedian. You were in Monty Python.'
Format Specifiers:
# Rounding
print(f'The value of pi is approximately {math.pi:.3f}.')
# The value of pi is approximately 3.142.
# Padding
table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
for name, phone in table.items():
print(f'{name:10} ==> {phone:10d}')
Sjoerd ==> 4127
Jack ==> 4098
Dcab ==> 7678
Other modifiers can be used to convert the value before it is formatted:
‘!a’ applies ascii()
‘!s’ applies str()
‘!r’ applies repr()
Template Strings¶
Note
Template strings don’t allow format specifiers, so you’ll have to manually tranform formats
from string import Template
t = Template('Hey, $name!')
t.substitute(name=name)
# 'Hey, Bob!'
# Manual transform
templ_string = 'Hey $name, there is a $error error!'
Template(templ_string).substitute(name=name, error=hex(errno))
# 'Hey Bob, there is a 0xbadc0ffee error!'
# Safe Substitute
# Uses original placeholder instead of rasing KeyError on missing arg(s)
from string import Template
s = Template('$who likes $what')
d = dict(who='tim')
Template('$who likes $what').safe_substitute(d)
# 'tim likes $what'