PEP 498: The Monologue

PEP 498: the Monologue Mariatta Wijaya @mariatta PyCon Australia 2017 @pyconau

Who are you? Hello! !

Are you … … new to Python?

Are you … … only familiar with one PEP?

Are you … … using Python < 3.6?

Who am I?

PyLadies Vancouver Co-Organizer Python Core Developer @mariatta

What’s a PEP?

P ython E nhancement P roposal

PEP 1: PEP Purpose and Guideline https://www.python.org/dev/peps/pep-0001

" pitch to python-ideas

draft a PEP Official template: PEP 12 alt template: pep_cookiecutter $%

& BDFL Pronouncement ' (

429 PEPs today 82 rejected (~19%)

PEP 498

Have long wished python could format strings easily like bash or perl do … and then it hit me From: Mike Miller Subject: [python-ideas] Briefer string format Jul 20 01:12:31 CEST 2015 csstext += f'{nl}{selector}{space}{{{nl}' I've seen others make similar suggestions, but to my knowledge they didn’t include this pleasing brevity aspect . https://mail.python.org/pipermail/python-ideas/2015-July/034657.html

From: Eric V. Smith Subject: Re: [python-ideas] Briefer string format Jul 20 01:12:31 CEST 2015 Jul 20 01:27:42 CEST 2015 What would this do? https://mail.python.org/pipermail/python-ideas/2015-July/034658.html

From: C. A. Subject: Re: [python-ideas] Briefer string format Jul 20 01:12:31 CEST 2015 https://mail.python.org/pipermail/python-ideas/2015-July/034660.html I’m -1 on the specific idea, though definitely sympathetic to the broader concept of simplified formatting of strings. Jul 20 01:44:09 CEST 2015 Jul 20 01:27:42 CEST 2015

From: S. D. Subject: Re: [python-ideas] Briefer string format It’s syntactic sugar

for a simple function call with perfectly well defined semantics - don’t even have to modify the string literal. I’m

+1 . Jul 20 01:12:31 CEST 2015 Jul 20 01:27:42 CEST 2015 Jul 20 01:44:09 CEST 2015 Jul 20 02:43:29 CEST 2015 https://mail.python.org/pipermail/python-ideas/2015-July/034669.html

that escalated quickly ( 60+ replies later)

From: Guido van Rossum Subject: Re: [python-ideas] Briefer string format Jul 20 01:12:31 CEST 2015 Jul 20 01:27:42 CEST 2015 Jul 20 01:44:09 CEST 2015 Jul 20 02:43:29 CEST 2015 Jul 21 08:05:17 CEST 2015 Thanks, Eric! You’re addressing all my concerns and you’re going exactly where I wanted this to go. I hope that you will find the time to write up a PEP; https://mail.python.org/pipermail/python-ideas/2015-July/034729.html

PEP 498: Literal String Formatting by: Eric V. Smith August 7th, 2015

PEP 498: Literal String Interpolation August 7th, 2015 August 30th, 2015 by: Eric V. Smith

PEP 498: Literal String Interpolation ready for pronouncement August 7th, 2015 August 30th, 2015 September 5th, 2015

PEP 498: Literal String Interpolation August 7th, 2015 August 30th, 2015 September 7th, 2015 September 5th, 2015

“The existing ways of formatting are either error prone , inflexible , or cumbersome .” RATIONALE

name = "Bart"

print( "Hello, %s ." % name) Hello, Bart.

name = "Bart"

age =

10

print( "Hello,

%s . You’re %s ."

% name, age ) Traceback (most recent call last):

File "<stdin>", line 1, in <module>

TypeError: not enough arguments for format string

name = "Bart"

age = 10

print( "Hello, %s . You’re %s ." %

( name, age ) ) Hello, Bart. You're 10.

PEP 3101: str.format https://www.python.org/dev/peps/pep-3101

name = "Bart"

age = 10

print( "Hello,

{name} . You’re {age} . " .format( name =name, age =age)) Hello, Bart. You're 10.

PEP 498: f-string https://www.python.org/dev/peps/pep-0498

name = "Bart"

age = 10

print( "Hello,

{name} . You’re {age} . " .format( name =name, age =age))

name = "Bart"

age = 10

print( "Hello,

{name} . You’re {age} . " )

name = "Bart"

age = 10

print( f "Hello, {name} . You’re

{age} ." ) Hello, Bart. You're 10.

Recap

"Hello, %s . You’re %s . " % (name, age ) "Hello, {name} . You’re {age} ." .format( name= name, age= age) f " Hello, {name} . You’re {age} . "

f " Hello, {name} . You’re {age} . "

expression

f " Hello, {name} . You’re {age} . "

literal

f "..."

✅ F' ...'

✅ f """..."""

✅

✅

r + f = fr " … " Raw f-strings

print( "The smiley face emoji is \U0001f600" ) The smiley face emoji is *

print( r "The smiley face unicode is \U0001f600" ) The smiley face unicode is \U0001f600

code = "emoji "

print( f"The smiley face {code} is \U0001f600" ) The smiley face emoji is *

code = "unicode "

print( f r "The smiley face {code} is \U0001f600" ) The smiley face unicode is \U0001f600

fr "..."

✅ RF "..."

✅ rF """..."""

✅

fb "..."

❌ uf "..."

❌

def to_uppercase(input): ... return input.upper() ...

name = "bart simpson"

print( f"Hi {to_uppercase(name)} !" ) Hi BART SIMPSON!

pi = 3.14159265

print( "pi 3 decimal places %.3f " % pi )

3.142

print( f"pi 3 decimal places {pi:.3f} " )

3.142

number =

1024

print( f"hex: {number:#0x} " )

hex: 0x400

print( f"binary: {number:#0b} " )

binary: 0b10000000000

print( f"octal: {number:#0o} " )

octal: 0o2000

pycon_au = datetime ( year= 2017, month= 8, day= 5)

print( f" {pycon_au:%b %d, %Y} " )

Aug 05, 2017

print( f" {name:>20} " )

            Bart

print( f" {age:=+5d} " )

10

❌

not in docstrings

def spam(): ...
f " doing stuff ”

...

spam. doc is None True bpo-28739

,

multiline strings?

name = "Bart"

prize = 50

tomorrow =

today() + timedelta( days= 1 )

message = ( f "Dear {name} ,"

... “You can win {prize:.2f} $"

... "Make a purchase before {tomorrow:%Y-%b-%d} " )

bpo-29668

✅

multiline strings

message = ( f "Dear {name} ,"

... f ”You can win {prize:.2f} $"

... f "Make a purchase before {tomorrow}:%Y-%b-%d " )

bpo-29668

IDLE needs syntax highlighting bpo-29287 • Needs separate colorization to make the expression distinct from the rest of the string. • Needs close-brace matching. • Would be desirable to have autocompletion as well.

.

Documentation … ? /

.

Documentation https://docs.python.org/3/reference/lexical_analysis.html#formatted-string-literals ⭐ 1 Formatted String Literal 2 docs.python.org

glossary

f-string

⏱

timeit

$ python3 -mtimeit -s 'a= 2 ' "'%s' % a " 10000000 loops, best of 3: 0.197

usec per loop

$ python3 -mtimeit -s 'a= 2 ' ' "{}" .format(a)' 1000000 loops, best of 3: 0.341 usec per loop $ python3 -mtimeit -s 'a=2' "'%s' % a" 10000000 loops, best of 3: 0.197

usec per loop

$ python3 -mtimeit -s 'a= 2 ' ' f" {a} " ' 10000000 loops, best of 3: 0.105 usec per loop $ python3 -mtimeit -s 'a=2' "'%s' % a" $ python3 -mtimeit -s 'a=2' '"{}".format(a)' 1000000 loops, best of 3:

0.341

usec per loop 10000000 loops, best of 3: 0.197

usec per loop

$ python3 -mtimeit -s 'a=2' ' f" {a} " ' 10000000 loops, best of 3: 0.105

usec per loop $ python3 -mtimeit -s 'a=2' "'%s' % a" $ python3 -mtimeit -s 'a=2' '"{}".format(a)' 1000000 loops, best of 3:

0.341

usec per loop 10000000 loops, best of 3: 0.197

usec per loop

PEP 498

f-strings

Python 3.6 download at www.python.org

4

bonus!

16 PEPs included PEP 468 PEP 487 PEP 495 PEP 498 PEP 506 PEP 509 PEP 515 PEP 519 PEP 520 PEP 523 PEP 524 PEP 525 PEP 526 PEP 528 PEP 529 PEP 530

Thank you! Mariatta Wijaya @mariatta | mariatta@python.org

File bugs at

https://bugs.python.org PyCon Australia 2017 @pyconau