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https://github.com/QuantStack/py2vega
https://github.com/QuantStack/py2vega
Last synced: 3 months ago
JSON representation
- Host: GitHub
- URL: https://github.com/QuantStack/py2vega
- Owner: QuantStack
- License: bsd-3-clause
- Created: 2019-08-19T07:15:29.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2021-03-03T09:46:55.000Z (over 3 years ago)
- Last Synced: 2024-07-14T13:32:53.846Z (4 months ago)
- Language: Python
- Size: 81.1 KB
- Stars: 9
- Watchers: 14
- Forks: 3
- Open Issues: 6
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- awesome-starred - QuantStack/py2vega - (others)
README
# py2vega
[](https://travis-ci.org/QuantStack/py2vega)
[](https://gitter.im/QuantStack/Lobby)
A Python to [Vega-expression](https://vega.github.io/vega/docs/expressions/) transpiler.
## Installation
### From PyPi
```bash
pip install py2vega
```
### From conda-forge
```bash
conda install -c conda-forge py2vega
```
### From sources
You can install from sources using `pip`:
```bash
git clone https://github.com/QuantStack/py2vega
cd py2vega
pip install .
```
## Usage
`py2vega` provides a `py2vega` function that turns a Python string code or a Python function into a valid [Vega-expression](https://vega.github.io/vega/docs/expressions/). Because it is turning the Python code into a [Vega-expression](https://vega.github.io/vega/docs/expressions/), only a subset of Python is supported: the `if` and `return` statements, the ternary operator, the `in` operator and types like `str`, `bool`, `dict`, `tuple`...
```Python
from py2vega import py2vega
def foo(value):
if value < 3:
return 'red'
elif value < 5:
return 'green'
else:
return 'yellow'
py2vega(foo, whitelist=['value']) # "if(value < 3, 'red', if(value < 5, 'green', 'yellow'))"
```
`py2vega` also provides functions and constants the same way they are available for vega-expressions:
```Python
from py2vega import py2vega
from py2vega.functions.math import isNaN
from py2vega.functions.string import lower
def foo(value):
if isNaN(value):
return lower('It is NaN...')
else:
return value
py2vega(foo, whitelist=['value']) # "if(isNaN(value), lower('It is NaN...'), value)"
```
Even if assignments are prohibited in [Vega-expressions](https://vega.github.io/vega/docs/expressions/), you can assign variables in your Python function, it will be turned into a valid [Vega-expression](https://vega.github.io/vega/docs/expressions/) anyway:
```Python
from py2vega import py2vega
def foo(value):
a = 'green'
b = 'red'
return a if value < 3 else b
py2vega(foo, whitelist=['value']) # "value < 3 ? 'green' : 'red'"
```
You can provide a variable whitelist as a list of strings, each string being an available variable. You can also allow member access using the `Variable` class from py2vega:
```Python
from py2vega import py2vega, Variable
py2vega('3 if value > 0 else 4', whitelist=['value']) # Returns "value > 0 ? 3 : 4"
py2vega('3 if my_variable > 0 else 4', whitelist=['value']) # Raises a SyntaxError, `my_variable` is not whitelisted
py2vega('3 if value.member1 > value.member2 else 4', whitelist=[Variable('value', ['member1', 'member2'])]) # Returns "value.member1 > value.member2 ? 3 : 4"
py2vega('3 if value.member3 > 0 else 4', whitelist=[Variable('value', ['member1', 'member2'])]) # Raises a SyntaxError, `value.member3` is not whitelisted`
```
Because of the way [Vega-expressions](https://vega.github.io/vega/docs/expressions/) are defined, there are some rules that must follow your Python function:
- the function body __must__ end with an `if` __or__ `return` statement and __cannot__ contain more than one `if` __or__ `return` statement
- `if` statements __can__ be followed by `elif` statements but __must__ be followed by an `else` statement
- the `if`/`elif`/`else` body __must__ end with an `if` __or__ `return` statement and __cannot__ contain more than one `if` __or__ `return` statement
If one of those rules is not respected, a Python `RuntimeError` will be raised.