A simple Result type for Python 3 inspired by Rust.
The idea is that a Result
value can be either Ok(value)
or Err(error)
,
with a way to differentiate between the two. It will change code like this:
def get_user_by_email(email):
"""
Return the user instance or an error message.
"""
if not user_exists(email):
return None, 'User does not exist'
if not user_active(email):
return None, 'User is inactive'
user = get_user(email)
return user, None
user, reason = get_user_by_email('ueli@example.com')
if user is None:
raise RuntimeError('Could not fetch user: %s' % reason)
else:
do_something(user)
To something like this:
from result import Ok, Err
def get_user_by_email(email):
"""
Return the user instance or an error message.
"""
if not user_exists(email):
return Err('User does not exist')
if not user_active(email):
return Err('User is inactive')
user = get_user(email)
return Ok(user)
user_result = get_user_by_email(email)
if user_result.is_ok():
do_something(user_result.value)
else:
raise RuntimeError('Could not fetch user: %s' user_result.value)
As this is Python and not Rust, you will lose some of the advantages that it
brings, like elegant combinations with the match
statement. On the other
side, you don't have to return semantically unclear tuples anymore.
Not all methods (https://doc.rust-lang.org/std/result/enum.Result.html) have been implemented, only the ones that make sense in the Python context. You still don't get any type safety, but some easier handling of types that can be OK or not, without resorting to custom exceptions.
Creating an instance:
>>> from result import Ok, Err >>> res1 = Ok('yay') >>> res2 = Err('nay')
Or through the class methods:
>>> from result import Result >>> res1 = Result.Ok('yay') >>> res2 = Result.Err('nay')
Checking whether a result is ok or not:
>>> res = Ok('yay') >>> res.is_ok() True >>> res.is_err() False
Convert a Result to the value or None
:
>>> res1 = Ok('yay') >>> res2 = Err('nay') >>> res1.ok() 'yay' >>> res2.ok() None
Convert a Result to the error or None
:
>>> res1 = Ok('yay') >>> res2 = Err('nay') >>> res1.err() None >>> res2.err() 'nay'
Access the value directly, without any other checks (like unwrap()
in Rust):
>>> res1 = Ok('yay') >>> res2 = Err('nay') >>> res1.value 'yay' >>> res2.value 'nay'
Note that this is a property, you cannot assign to it. Results are immutable.
For your convenience, simply creating an Ok result without value is the same as using True:
>>> res1 = Result.Ok() >>> res1.value True >>> res2 = Ok() >>> res2.value True
In case you're missing methods like unwrap_or(default)
, these can be
achieved by regular Python constructs:
>>> res1 = Ok('yay') >>> res2 = Err('nay') >>> res1.ok() or 'default' 'yay' >>> res2.ok() or 'default' 'default'
MIT License