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cel-python-0.1.5
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Pure Python CEL Implementation
| ویژگی | مقدار |
|---|---|
| سیستم عامل | - |
| نام فایل | cel-python-0.1.5 |
| نام | cel-python |
| نسخه کتابخانه | 0.1.5 |
| نگهدارنده | [] |
| ایمیل نگهدارنده | [] |
| نویسنده | Cloud Custodian Project |
| ایمیل نویسنده | - |
| آدرس صفحه اصلی | https://github.com/cloud-custodian/cel-python |
| آدرس اینترنتی | https://pypi.org/project/cel-python/ |
| مجوز | Apache-2.0 |
##########
cel-python
##########
.. image:: https://travis-ci.org/cloud-custodian/cel-python.svg?branch=master
:target: https://travis-ci.org/cloud-custodian/cel-python
:alt: Travis Build Status
.. image:: https://requires.io/github/cloud-custodian/cel-python/requirements.svg?branch=master
:target: https://requires.io/github/cloud-custodian/cel-python/requirements/?branch=master
:alt: Requirements Status
.. image:: https://img.shields.io/badge/license-Apache%202-blue.svg
:target: https://www.apache.org/licenses/LICENSE-2.0
:alt: Apache License
Pure Python implementation of Google Common Expression Language, https://opensource.google/projects/cel.
The Common Expression Language (CEL) implements common semantics for expression evaluation,
enabling different applications to more easily interoperate.
Key Applications
Security policy: organization have complex infrastructure and need common tooling to reason about the system as a whole
Protocols: expressions are a useful data type and require interoperability across programming languages and platforms.
This implementation has minimal dependencies, runs quickly, and can be embedded into Python-based applications.
Specifically, the intent is to be part of Cloud Custodian, C7N, as part of the security policy filter.
Installation
=============
::
pip install cel-python
You now have the CEL run-time available to Python-based applications.
Command Line
============
We can read JSON directly from stdin, making this a bit like ``jq``.
::
% python -m celpy '.this.from.json * 3 + 3' <<EOF
heredoc> {"this": {"from": {"json": 13}}}
heredoc> EOF
42
It's also a desk calculator, like ``expr``, but with float values:
::
% python -m celpy -n '355.0 / 113.0'
3.1415929203539825
It's not as sophistcated as ``bc``.
But, yes, this has a tiny advantage over ``python -c '355/113'``. Most notably, the ability
to embed Google CEL into other contexts where you don't *really* want Python's power.
It's also capable of decision-making, like ``test``:
::
% echo '{"status": 3}' | python -m celpy -sb '.status == 0'
false
% echo $?
1
We can provide a ``-a`` option to define objects with specific data types.
This is particularly helpful for providing protobuf message definitions.
::
python -m celpy -n --arg x:int=6 --arg y:int=7 'x*y'
42
If you want to see details of evaluation, use ``-v``.
::
python -m celpy -v -n '[2, 4, 6].map(n, n/2)'
... a lot of output
[1, 2, 3]
Library
=======
To follow the pattern defined in the Go implementation, there's a multi-step
process for compiling a CEL expression to create a runnable "program". This program
can then be applied to argument values.
::
>>> import celpy
>>> cel_source = """
... account.balance >= transaction.withdrawal
... || (account.overdraftProtection
... && account.overdraftLimit >= transaction.withdrawal - account.balance)
... """
>>> env = celpy.Environment()
>>> ast = env.compile(cel_source)
>>> prgm = env.program(ast)
>>> activation = {
... "account": celpy.json_to_cel({"balance": 500, "overdraftProtection": False}),
... "transaction": celpy.json_to_cel({"withdrawal": 600})
... }
>>> result = prgm.evaluate(activation)
>>> result
BoolType(False)
The Python classes are generally based on the object model in https://github.com/google/cel-go
These types semantics are slightly different from Python's native semantics.
Type coercion is not generally done.
Python ``//`` truncates toward negative infinity. Go (and CEL) ``/`` truncates toward zero.
Development
===========
The parser is based on the grammars used by Go and C++, but processed through Python Lark.
See https://github.com/google/cel-spec/blob/master/doc/langdef.md
https://github.com/google/cel-cpp/blob/master/parser/Cel.g4
https://github.com/google/cel-go/blob/master/parser/gen/CEL.g4
Notes
=====
CEL provides a number of runtime errors that are mapped to Python exceptions.
- ``no_matching_overload``: this function has no overload for the types of the arguments.
- ``no_such_field``: a map or message does not contain the desired field.
- ``return error for overflow``: integer arithmetic overflows
There are mapped to Python ``celpy.evaluation.EvalError`` exception. The args will have
a message similar to the CEL error message, as well as an underlying Python exception.
In principle CEL can pre-check types.
However, see https://github.com/google/cel-spec/blob/master/doc/langdef.md#gradual-type-checking.
Rather than try to pre-check types, we'll rely on Python's implementation.
Contributing
============
See https://cloudcustodian.io/docs/contribute.html
Code of Conduct
===============
This project adheres to the `Open Code of Conduct <https://developer.capitalone.com/resources/code-of-conduct>`_. By
participating, you are expected to honor this code.
نیازمندی
| مقدار | نام |
|---|---|
| >=0.10.0 | jmespath |
| >=0.10.1 | lark-parser |
| >=2.8.1 | python-dateutil |
| >=5.4.1 | pyyaml |
| >=2.25.1 | requests |
| >=1.26.4 | urllib3 |
| >=2.9.0 | babel |
زبان مورد نیاز
| مقدار | نام |
|---|---|
| >=3.7, <4 | Python |
نحوه نصب
نصب پکیج whl cel-python-0.1.5:
pip install cel-python-0.1.5.whl
نصب پکیج tar.gz cel-python-0.1.5:
pip install cel-python-0.1.5.tar.gz