Resetting bytearray

[danielm]

How to "reset" bytearray (set all bytes to b'\x00') without being re-allocated?

After doing this function id() should return same value as before.

[deshipu]

The obvious solution would be:

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for i in range(len(your_array)):
    your_array[i] = 0

[platforma]

One more option is

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arr[:] = b'0' * len(arr)

[kfricke]

One more option is

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arr[:] = b'0' * len(arr)

Does this really not re-allocate the buffer?

[platforma]

At least not from what I tried on unix port:

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>>> arr = bytearray([1,2,3])
>>> arr
bytearray(b'\x01\x02\x03')
>>> id(arr)
140355047877312
>>> arr[:] = b'0' * len(arr)
>>> arr
bytearray(b'000')
>>> id(arr)
140355047877312

[deshipu]

It allocates a new buffer, and then copies it over to the old one.

[deshipu]

The below code could be much more memory-efficient, unfortunately it's not working:

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>>> a[:] = (b'0' for i in range(10))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NotImplementedError: array/bytes required on right side

[markxr]

I used:

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tempbuf = bytearray() 

# ...

tempbuf[::] = b''

Is that ok, or not?

[deshipu]

No, that truncates the array to make it 0-element long.

[pythoncoder]

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$ ./upython 
MicroPython v1.8.1-39-gdb4addd on 2016-07-01; linux version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> a = bytearray(10)
>>> id(a)
139728051341376
>>> a[:] = b'\1' * len(a)
>>> id(a)
139728051341376
>>> a
bytearray(b'\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01')
>>> a[:] = b'\0' * len(a)
>>> a
bytearray(b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')
>>> id(a)
139728051341376
>>> 

While this preserves the ID, I assume a bytes object is temporarily allocated before being copied to the original. Aside from the original suggestion from @deshipu I can see two ways to avoid allocation. One, if speed is critical, would be to implement the original solution using inline assembler. The other would be to define a bytes instance for copying and freeze it as bytecode.