Thanks Stefano, that makes it a bit clearer. However I have been
playing around writing to an alias and I really don't understand what is
happening.
For some reason I cannot write 'T0' (that's tee zero) to the alias. I
don't understand why. Here is what I have seen -
>>> import pyownet
>>> owp = pyownet.protocol.proxy()
>>> addr = '28.E3377A020000/alias'
>>> owp.read(addr).decode()
'xx'
>>> owp.write(addr, 'T0'.encode())
>>> owp.read(addr).decode()
'xx'
>>> owp.write(addr, 'T0'.encode())
>>> owp.read(addr).decode()
'xx'
>>> owp.write(addr, 'T0x'.encode())
>>> owp.read(addr).decode()
'T0x'
>>> owp.write(addr, 'T0'.encode())
>>> owp.read(addr).decode()
'T0x'
>>> owp.write(addr, 'T01'.encode())
>>> owp.read(addr).decode()
'T01'
>>> owp.write(addr, 'T0'.encode())
>>> owp.read(addr).decode()
'T01'
>>> owp.write(addr, 'T'.encode())
>>> owp.read(addr).decode()
'T'
>>> owp.write(addr, 'T0'.encode())
>>> owp.read(addr).decode()
'T'
>>> owp.write(addr, 'T00'.encode())
>>> owp.read(addr).decode()
'T00'
>>>
On 10/10/2019 15:04, Stefano Miccoli via Owfs-developers wrote:
I think that this is the correct place to ask, so I'll give a brief
answer.
In python2 you had "strings" and "unicode strings". Python2 "strings"
were 1-byte sequences, so it was impossibile to represent UNICODE code
points beyond the few ASCII ones; therefore the "unicode string" was
introduced. Strings could be used both for binary data, as well as for
text.
This confusion was deprecated, and in python3 there is a strict
distinction between text and binary data. Strings (see
<https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str>) are
sequences of UNICODE code points, and therefore are multi-byte
sequences; 1-byte (8 bit) sequences are called "bytes" (see
<https://docs.python.org/3/library/stdtypes.html#bytes-objects>) and
are used for binary data.
A very common mapping from python2 to python3 datatypes is
str() → byte()
unicode() → str()
or if you prefer
"abc" → b"abc"
u"àèì" → "àèì"
I regard pyownet as a low-level library, so I like to speak binary to
the owserver, i.e. read and writes are bytes in python3 and str in
python2. It is responsibility of the user to decode/encode the
messages sent and received from owserver. OWFS node names (similarly
to path names on a file system) instead are considered "non binary",
and therefore are represented by strings.
As what regards the practicality of using pyownet.
- some nodes contain binary data:
e.g. '/26.xxxxxxxxxxxx/pages/page.ALL', no decoding needed
- numeric values can be converted directly, without the need of
decoding: if owp is a proxy object you have e.g.
>>> owp.read('/26.xxxxxxxxxxxx/temperature')
b' 24.4688'
>>> float(owp.read('/26.xxxxxxxxxxxx/temperature'))
24.4688
(this is because the float() class accepts both strings and bytes as
input.)
- text values should be decoded, but usually you can omit the encoding
(which should be 'utf-8' or better 'ascii'):
>>> owp.read("/structure/26/CA")
b'y,000000,000001,rw,000001,s,'
>>> owp.read("/structure/26/CA").decode()
'y,000000,000001,rw,000001,s,'
Regards,
Stefano
On 9 Oct 2019, at 22:44, Mick Sulley <m...@sulley.info
<mailto:m...@sulley.info>> wrote:
I am updating my python code from 2.7 to 3.7, using pyownet to
communicate with 1-wire.
Reads and writes were strings in 2.7 but it seems they are binary in
3.7. I can get around this by appending .decode('utf-8) and
.encode('utf-8) to the read and write functions, but I feel that I am
making hard work of this. Is there a better way to move reads and
writes to Python3?
I don't understand why the change has occurred, but I guess that is
not a question for this group.
Thanks
Mick
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