This might not meet you criteria for being 'graceful', and it is very Python 2.6 specific, but it is quick and easy to do. Function annotations are a piece of syntax introduced in Python 3.0 that was not backported to Python 2.x. I suspect that as the error from the import isn't really a syntax error in itself it isn't raised on the first compilation pass, and so real syntax errors get raised first (but I'm guessing). You might think that as you will have to have this line after your from _future_ import print_function then it will be the import that generates the Synta圎rror and you won't get to see the useful error message, but strangely enough the later error takes precedence. Anyone trying to compile your file will still get an error, but they also get whatever message you want to give. This is harmless in Python 2.6 or later, but a Synta圎rror in any earlier versions. This snippet from the PEP seems to give hope of doing it inline:Ī rather hacky but simple method I've used before is to exploit the fact that byte literals were introduced in Python 2.6 and use something like this near the start of the file: b'This module needs Python 2.6 or later. Synta圎rror: from _future_ imports must occur at the beginning of the file Raise ImportError('Python >= 2.6 is required')īecause it yields: File "_init_.py", line 4 So I can't do something like: import _future_ I'd like to inform the user that they need to rerun the program with Python >= 2.6 and maybe provide some instructions on how to do so. Synta圎rror: future feature print_function is not defined def copy(self) -> Widget: return deepcopy(self) Python no longer interprets the type hints at runtime, so it doesn’t hit the NameError. In our example: from future import annotations from copy import deepcopy class Widget. See also PEP 563 and PEP 649.How do you gracefully handle failed future feature imports? If a user is running using Python 2.5 and the first statement in my module is: from _future_ import print_functionĬompiling this module for Python 2.5 will fail with a: File "_init_.py", line 1 We can opt into postponed evaluation in a file by adding from future import annotations at the top. Imports: Multi-Line and Absolute/Relativeįrom _future_ import annotations was previously scheduled toīecome mandatory in Python 3.10, but the Python Steering Council Introduction in Python 2.1 the following features have found their way into the No feature description will ever be deleted from _future_. GetOptionalRelease() and getMandatoryRelease().ĬompilerFlag is the (bitfield) flag that should be passed in the fourthĪrgument to the built-in function compile() to enable the feature inĭynamically compiled code. This can be done automatically with isort. Instances of class _Feature have two corresponding methods, Consider adding from future import annotations to all your files. MandatoryRelease may also be None, meaning that a planned feature got Releases at or after that, modules no longer need a future statement to use theįeature in question, but may continue to use such imports. MandatoryRelease predicts the release in which the feature will become part ofĮlse MandatoryRelease records when the feature became part of the language in In the case of a MandatoryRelease that has not yet occurred, Type hints allow you to specify types on function parameters, class attributes, and variables, which can later be statically type checked using tools like Mypy. PEP 484 introduced type hints back in 2014. OptionalRelease records the first release in which the feature was accepted. PEP 563, PEP 649, and the Future of Python Type Annotations. ( PY_MAJOR_VERSION, # the 2 in 2.1.0a3 an int PY_MINOR_VERSION, # the 1 an int PY_MICRO_VERSION, # the 0 an int PY_RELEASE_LEVEL, # "alpha", "beta", "candidate" or "final" string PY_RELEASE_SERIAL # the 3 an int ) In python doc about future there is a table below where it shows that annotations 'optional in' 3.7.0b1 and 'mandatory in' 4.0 but I am still able to use annotations in 3.8.2 without importing annotations then what is the use of it.
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