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Use in Python {#flatbuffers_guide_use_python}
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=============
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## Before you get started
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Before diving into the FlatBuffers usage in Python, it should be noted that the
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[Tutorial](@ref flatbuffers_guide_tutorial) page has a complete guide to general
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FlatBuffers usage in all of the supported languages (including Python). This
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page is designed to cover the nuances of FlatBuffers usage, specific to
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Python.
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You should also have read the [Building](@ref flatbuffers_guide_building)
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documentation to build `flatc` and should be familiar with
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[Using the schema compiler](@ref flatbuffers_guide_using_schema_compiler) and
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[Writing a schema](@ref flatbuffers_guide_writing_schema).
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## FlatBuffers Python library code location
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The code for the FlatBuffers Python library can be found at
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`flatbuffers/python/flatbuffers`. You can browse the library code on the
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[FlatBuffers GitHub page](https://github.com/google/flatbuffers/tree/master/
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python).
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## Testing the FlatBuffers Python library
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The code to test the Python library can be found at `flatbuffers/tests`.
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The test code itself is located in [py_test.py](https://github.com/google/
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flatbuffers/blob/master/tests/py_test.py).
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To run the tests, use the [PythonTest.sh](https://github.com/google/flatbuffers/
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blob/master/tests/PythonTest.sh) shell script.
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*Note: This script requires [python](https://www.python.org/) to be
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installed.*
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## Using the FlatBuffers Python library
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*Note: See [Tutorial](@ref flatbuffers_guide_tutorial) for a more in-depth
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example of how to use FlatBuffers in Python.*
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There is support for both reading and writing FlatBuffers in Python.
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To use FlatBuffers in your own code, first generate Python classes from your
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schema with the `--python` option to `flatc`. Then you can include both
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FlatBuffers and the generated code to read or write a FlatBuffer.
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For example, here is how you would read a FlatBuffer binary file in Python:
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First, import the library and the generated code. Then read a FlatBuffer binary
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file into a `bytearray`, which you pass to the `GetRootAsMonster` function:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.py}
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import MyGame.Example as example
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import flatbuffers
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buf = open('monster.dat', 'rb').read()
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buf = bytearray(buf)
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monster = example.GetRootAsMonster(buf, 0)
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Now you can access values like this:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.py}
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hp = monster.Hp()
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pos = monster.Pos()
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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## Support for Numpy arrays
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The Flatbuffers python library also has support for accessing scalar
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vectors as numpy arrays. This can be orders of magnitude faster than
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iterating over the vector one element at a time, and is particularly
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useful when unpacking large nested flatbuffers. The generated code for
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a scalar vector will have a method `<vector name>AsNumpy()`. In the
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case of the Monster example, you could access the inventory vector
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like this:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.py}
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inventory = monster.InventoryAsNumpy()
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# inventory is a numpy array of type np.dtype('uint8')
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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instead of
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.py}
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inventory = []
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for i in range(monster.InventoryLength()):
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inventory.append(int(monster.Inventory(i)))
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Numpy is not a requirement. If numpy is not installed on your system,
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then attempting to access one of the `*asNumpy()` methods will result
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in a `NumpyRequiredForThisFeature` exception.
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## Text Parsing
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There currently is no support for parsing text (Schema's and JSON) directly
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from Python, though you could use the C++ parser through SWIG or ctypes. Please
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see the C++ documentation for more on text parsing.
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<br>
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