asottile/pyupgrade: A tool (and pre-commit hook) to automatically upgrade syntax for newer versions of the language.

pip install pyupgrade

See pre-commit for instructions

Sample .pre-commit-config.yaml:

-   repo: https://github.com/asottile/pyupgrade
    rev: v3.22.0
    hooks:
    -   id: pyupgrade

Implemented features

Set literals

-set(())
+set()
-set([])
+set()
-set((1,))
+{1}
-set((1, 2))
+{1, 2}
-set([1, 2])
+{1, 2}
-set(x for x in y)
+{x for x in y}
-set([x for x in y])
+{x for x in y}

Dictionary comprehensions

-dict((a, b) for a, b in y)
+{a: b for a, b in y}
-dict([(a, b) for a, b in y])
+{a: b for a, b in y}

Replace unnecessary lambdas in collections.defaultdict calls

-defaultdict(lambda: [])
+defaultdict(list)
-defaultdict(lambda: list())
+defaultdict(list)
-defaultdict(lambda: {})
+defaultdict(dict)
-defaultdict(lambda: dict())
+defaultdict(dict)
-defaultdict(lambda: ())
+defaultdict(tuple)
-defaultdict(lambda: tuple())
+defaultdict(tuple)
-defaultdict(lambda: set())
+defaultdict(set)
-defaultdict(lambda: 0)
+defaultdict(int)
-defaultdict(lambda: 0.0)
+defaultdict(float)
-defaultdict(lambda: 0j)
+defaultdict(complex)
-defaultdict(lambda: '')
+defaultdict(str)

Format Specifiers

-'{0} {1}'.format(1, 2)
+'{} {}'.format(1, 2)
-'{0}' '{1}'.format(1, 2)
+'{}' '{}'.format(1, 2)

printf-style string formatting

Availability:

• Unless --keep-percent-format is passed.

-'%s %s' % (a, b)
+'{} {}'.format(a, b)
-'%r %2f' % (a, b)
+'{!r} {:2f}'.format(a, b)
-'%(a)s %(b)s' % {'a': 1, 'b': 2}
+'{a} {b}'.format(a=1, b=2)

Unicode literals

-u'foo'
+'foo'
-u"foo"
+'foo'
-u'''foo'''
+'''foo'''

Invalid escape sequences

# strings with only invalid sequences become raw strings
-'\d'
+r'\d'
 # strings with mixed valid / invalid sequences get escaped
-'\n\d'
+'\n\\d'
-u'\d'
+r'\d'
 # this fixes a syntax error in python3.3+
-'\N'
+r'\N'

is / is not comparison to constant literals

In python3.8+, comparison to literals becomes a SyntaxWarning as the success of those comparisons is implementation specific (due to common object caching).

-x is 5
+x == 5
-x is not 5
+x != 5
-x is 'foo'
+x == 'foo'

.encode() to bytes literals

-'foo'.encode()
+b'foo'
-'foo'.encode('ascii')
+b'foo'
-'foo'.encode('utf-8')
+b'foo'
-u'foo'.encode()
+b'foo'
-'\xa0'.encode('latin1')
+b'\xa0'

extraneous parens in print(...)

A fix for [python-modernize/python-modernize#178]

# ok: printing an empty tuple
 print(())
 # ok: printing a tuple
 print((1,))
 # ok: parenthesized generator argument
 sum((i for i in range(3)), [])
 # fixed:
-print(("foo"))
+print("foo")

[python-modernize/python-modernize#178]: https://github.com/python-modernize/python-modernize/issues/178

constant fold isinstance / issubclass / except

-isinstance(x, (int, int))
+isinstance(x, int)
-issubclass(y, (str, str))
+issubclass(y, str)
try:
     raises()
-except (Error1, Error1, Error2):
+except (Error1, Error2):
     pass

unittest deprecated aliases

Rewrites deprecated unittest method aliases to their non-deprecated forms.

from unittest import TestCase
class MyTests(TestCase):
     def test_something(self):
self.failUnlessEqual(1, 1)
+        self.assertEqual(1, 1)
self.assertEquals(1, 1)
+        self.assertEqual(1, 1)

super() calls

class C(Base):
     def f(self):
super(C, self).f()
+        super().f()

"new style" classes

rewrites class declaration

-class C(object): pass
+class C: pass
-class C(B, object): pass
+class C(B): pass

removes __metaclass__ = type declaration

class C:
__metaclass__ = type

forced str("native") literals

-str()
+''
-str("foo")
+"foo"

.encode("utf-8")

-"foo".encode("utf-8")
+"foo".encode()

# coding: ... comment

as of [PEP 3120], the default encoding for python source is UTF-8

-# coding: utf-8
 x = 1

[PEP 3120]: https://www.python.org/dev/peps/pep-3120/

__future__ import removal

Availability:

• by default removes nested_scopes, generators, with_statement,

• --py37-plus will also remove generator_stop

-from __future__ import with_statement

Remove unnecessary py3-compat imports

-from io import open
-from six.moves import map
-from builtins import object  # python-future

import replacements

Availability:

• --py36-plus (and others) will replace imports

some examples:

-from collections import deque, Mapping
+from collections import deque
+from collections.abc import Mapping

-from typing import Sequence
+from collections.abc import Sequence

-from typing_extensions import Concatenate
+from typing import Concatenate

rewrite mock imports

Availability:

• Unless --keep-mock is passed on the commandline.

-from mock import patch
+from unittest.mock import patch

yield => yield from

def f():
for x in y:
yield x
+    yield from y
for a, b in c:
yield (a, b)
+    yield from c

Python2 and old Python3.x blocks

import sys
-if sys.version_info < (3,):  # also understands six.PY2 (and not), six.PY3 (and not)
print('py2')
-else:
print('py3')
+print('py3')

Availability:

• --py36-plus will remove Python <= 3.5 only blocks
• --py37-plus will remove Python <= 3.6 only blocks
• so on and so forth

# using --py36-plus for this example

import sys
-if sys.version_info < (3, 6):
print('py3.5')
-else:
print('py3.6+')
+print('py3.6+')

-if sys.version_info <= (3, 5):
print('py3.5')
-else:
print('py3.6+')
+print('py3.6+')

-if sys.version_info >= (3, 6):
print('py3.6+')
-else:
print('py3.5')
+print('py3.6+')

Note that if blocks without an else will not be rewritten as it could introduce a syntax error.

versioned @pytest.mark.skipif decorators

similar to above: redundant skipif marks are removed.

[email protected](sys.version_info < (3, 6), reason="py36+")
 def test_func():
     ...

remove six compatibility code

-six.text_type
+str
-six.binary_type
+bytes
-six.class_types
+(type,)
-six.string_types
+(str,)
-six.integer_types
+(int,)
-six.unichr
+chr
-six.iterbytes
+iter
-six.print_(...)
+print(...)
-six.exec_(c, g, l)
+exec(c, g, l)
-six.advance_iterator(it)
+next(it)
-six.next(it)
+next(it)
-six.callable(x)
+callable(x)
-six.moves.range(x)
+range(x)
-six.moves.xrange(x)
+range(x)
-from six import text_type
-text_type
+str
[email protected]_2_unicode_compatible
 class C:
     def __str__(self):
         return u'C()'
-class C(six.Iterator): pass
+class C: pass
-class C(six.with_metaclass(M, B)): pass
+class C(B, metaclass=M): pass
[email protected]_metaclass(M)
-class C(B): pass
+class C(B, metaclass=M): pass
-isinstance(..., six.class_types)
+isinstance(..., type)
-issubclass(..., six.integer_types)
+issubclass(..., int)
-isinstance(..., six.string_types)
+isinstance(..., str)
-six.b('...')
+b'...'
-six.u('...')
+'...'
-six.byte2int(bs)
+bs[0]
-six.indexbytes(bs, i)
+bs[i]
-six.int2byte(i)
+bytes((i,))
-six.iteritems(dct)
+dct.items()
-six.iterkeys(dct)
+dct.keys()
-six.itervalues(dct)
+dct.values()
-next(six.iteritems(dct))
+next(iter(dct.items()))
-next(six.iterkeys(dct))
+next(iter(dct.keys()))
-next(six.itervalues(dct))
+next(iter(dct.values()))
-six.viewitems(dct)
+dct.items()
-six.viewkeys(dct)
+dct.keys()
-six.viewvalues(dct)
+dct.values()
-six.create_unbound_method(fn, cls)
+fn
-six.get_unbound_function(meth)
+meth
-six.get_method_function(meth)
+meth.__func__
-six.get_method_self(meth)
+meth.__self__
-six.get_function_closure(fn)
+fn.__closure__
-six.get_function_code(fn)
+fn.__code__
-six.get_function_defaults(fn)
+fn.__defaults__
-six.get_function_globals(fn)
+fn.__globals__
-six.raise_from(exc, exc_from)
+raise exc from exc_from
-six.reraise(tp, exc, tb)
+raise exc.with_traceback(tb)
-six.reraise(*sys.exc_info())
+raise
-six.assertCountEqual(self, a1, a2)
+self.assertCountEqual(a1, a2)
-six.assertRaisesRegex(self, e, r, fn)
+self.assertRaisesRegex(e, r, fn)
-six.assertRegex(self, s, r)
+self.assertRegex(s, r)
# note: only for literals
-six.ensure_binary('...')
+b'...'
-six.ensure_str('...')
+'...'
-six.ensure_text('...')
+'...'

open alias

-with io.open('f.txt') as f:
+with open('f.txt') as f:
     ...

redundant open modes

-open("foo", "U")
+open("foo")
-open("foo", "Ur")
+open("foo")
-open("foo", "Ub")
+open("foo", "rb")
-open("foo", "rUb")
+open("foo", "rb")
-open("foo", "r")
+open("foo")
-open("foo", "rt")
+open("foo")
-open("f", "r", encoding="UTF-8")
+open("f", encoding="UTF-8")
-open("f", "wt")
+open("f", "w")

OSError aliases

# also understands:
 # - IOError
 # - WindowsError
 # - mmap.error and uses of from mmap import error
 # - select.error and uses of from select import error
 # - socket.error and uses of from socket import error
def throw():
raise EnvironmentError('boom')
+    raise OSError('boom')

def catch():
     try:
         throw()
except EnvironmentError:
+    except OSError:
         handle_error()

TimeoutError aliases

Availability:

• --py310-plus for socket.timeout
• --py311-plus for asyncio.TimeoutError

def throw(a):
     if a:
raise asyncio.TimeoutError('boom')
+        raise TimeoutError('boom')
     else:
raise socket.timeout('boom')
+        raise TimeoutError('boom')

def catch(a):
     try:
         throw(a)
except (asyncio.TimeoutError, socket.timeout):
+    except TimeoutError:
         handle_error()

typing.Text str alias

-def f(x: Text) -> None:
+def f(x: str) -> None:
     ...

Unpacking list comprehensions

-foo, bar, baz = [fn(x) for x in items]
+foo, bar, baz = (fn(x) for x in items)

Rewrite xml.etree.cElementTree to xml.etree.ElementTree

-import xml.etree.cElementTree as ET
+import xml.etree.ElementTree as ET
-from xml.etree.cElementTree import XML
+from xml.etree.ElementTree import XML

Rewrite type of primitive

-type('')
+str
-type(b'')
+bytes
-type(0)
+int
-type(0.)
+float

typing.NamedTuple / typing.TypedDict py36+ syntax

Availability:

• --py36-plus is passed on the commandline.

-NT = typing.NamedTuple('NT', [('a', int), ('b', Tuple[str, ...])])
+class NT(typing.NamedTuple):
+    a: int
+    b: Tuple[str, ...]

-D1 = typing.TypedDict('D1', a=int, b=str)
+class D1(typing.TypedDict):
+    a: int
+    b: str
-D2 = typing.TypedDict('D2', {'a': int, 'b': str})
+class D2(typing.TypedDict):
+    a: int
+    b: str

f-strings

Availability:

• --py36-plus is passed on the commandline.

-'{foo} {bar}'.format(foo=foo, bar=bar)
+f'{foo} {bar}'
-'{} {}'.format(foo, bar)
+f'{foo} {bar}'
-'{} {}'.format(foo.bar, baz.womp)
+f'{foo.bar} {baz.womp}'
-'{} {}'.format(f(), g())
+f'{f()} {g()}'
-'{x}'.format(**locals())
+f'{x}'

_note_: pyupgrade is intentionally timid and will not create an f-string if it would make the expression longer or if the substitution parameters are sufficiently complicated (as this can decrease readability).

subprocess.run: replace universal_newlines with text

Availability:

• --py37-plus is passed on the commandline.

-output = subprocess.run(['foo'], universal_newlines=True)
+output = subprocess.run(['foo'], text=True)

subprocess.run: replace stdout=subprocess.PIPE, stderr=subprocess.PIPE with capture_output=True

Availability:

• --py37-plus is passed on the commandline.

-output = subprocess.run(['foo'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+output = subprocess.run(['foo'], capture_output=True)

remove parentheses from @functools.lru_cache()

Availability:

• --py38-plus is passed on the commandline.

import functools

[email protected]_cache()
[email protected]_cache
 def expensive():
     ...

shlex.join

Availability:

• --py38-plus is passed on the commandline.

-' '.join(shlex.quote(arg) for arg in cmd)
+shlex.join(cmd)

replace @functools.lru_cache(maxsize=None) with shorthand

Availability:

• --py39-plus is passed on the commandline.

import functools

[email protected]_cache(maxsize=None)
[email protected]
 def expensive():
     ...

removeprefix / removesuffix

Availability:

• --py39-plus is passed on the commandline.

-if x.startswith(y):
x = x[len(y):]
+x = x.removeprefix(y)

-if x.endswith(y):
x = x[:-1 * len(y)]
+x = x.removesuffix(y)

pep 585 typing rewrites

Availability:

• File imports from __future__ import annotations

• --py39-plus is passed on the commandline.

-def f(x: List[str]) -> None:
+def f(x: list[str]) -> None:
     ...

pep 604 typing rewrites

Availability:

• File imports from __future__ import annotations

• --py310-plus is passed on the commandline.

-def f() -> Optional[str]:
+def f() -> str | None:
     ...

-def f() -> Union[int, str]:
+def f() -> int | str:
     ...

pep 696 TypeVar defaults

Availability:

• File imports from __future__ import annotations

• --py313-plus is passed on the commandline.

-def f() -> Generator[int, None, None]:
+def f() -> Generator[int]:
     yield 1

-async def f() -> AsyncGenerator[int, None]:
+async def f() -> AsyncGenerator[int]:
     yield 1

remove quoted annotations

Availability:

• File imports from __future__ import annotations

-def f(x: 'queue.Queue[int]') -> C:
+def f(x: queue.Queue[int]) -> C:

use datetime.UTC alias

Availability:

• --py311-plus is passed on the commandline.

import datetime

-datetime.timezone.utc
+datetime.UTC

sentinel

Availability:

• --py315-plus is passed on the commandline.

-_MISSING = object()
+_MISSING = sentinel('_MISSING')

utf-8 mode for open

Availability:

• --py315-plus is passed on the commandline.

-with open(fname, encoding="utf-8") as f:
+with open(fname) as f:

comprehension unpackings

Availability:

• --py315-plus is passed on the commandline.

-listcomp = [x for a in b for x in a]
+listcomp = [*a for a in b]
-setcomp = {x for a in b for x in a}
+setcomp = {*a for a in b}
-genexpr = (x for a in b for x in a)
+genexpr = (*a for a in b)
-dictcomp = {k: v for a in b for k, v in a.items()}
+dictcomp = {**a for a in b}

note: pyupgrade will rewrite non-nested redundant comprehensions independent of version:

-listcomp = [x for x in y]
+listcomp = [*y]

itertools.chain

Availability:

• --py315-plus is passed on the commandline.

-itertools.chain.from_iterable(x)
+(*it for it in x)
-itertools.chain(x)
+iter(x)
-itertools.chain(*x)
+(*it for it in x)
-itertools.chain(a, b, c)
+(*it for it in (a, b, c))

lazy-ify TYPE_CHECKING imports

Availability:

• --py315-plus is passed on the commandline.

-if TYPE_CHECKING:
from typing import Self
+lazy from typing import Self

remove ArgumentParser(suggest_on_error=True)

Availability:

• --py315-plus is passed on the commandline.

-parser = argparse.ArgumentParser(suggest_on_error=True)
+parser = argparse.ArgumentParser()