Client problem

[Youandi12]

We get this error from Python and don't know how to solve it.
We want to use the Python to write values in a DB(109). They are real.
We have no experience with the raspberry, so could you help us please?

Traceback (most recent call last):
File "/home/pi/testcom2.py", line 17, in
client = snap7.client.Client()
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 36, in init
self.create()
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 43, in create
self.library.Cli_Create.restype = c_void_p
AttributeError: 'NoneType' object has no attribute 'Cli_Create'

This is our programme:

import re
from ctypes import c_int, c_char_p, byref, sizeof, c_uint16, c_int32, c_byte
from ctypes import c_void_p

import logging

import snap7
from snap7 import six
from snap7.snap7types import S7Object, buffer_type, buffer_size, BlocksList
from snap7.snap7types import TS7BlockInfo, param_types, cpu_statuses

from snap7.common import check_error, load_library, ipv4
from snap7.snap7exceptions import Snap7Exception

logger = logging.getLogger(name)

client = snap7.client.Client()
client.connect('192.168.5.2', 0, 1)

class Client(object):
def db_write(self,db_number , start, data):
"""
Writes to a DB object.

    :param start: write offset
    :param data: bytearray
    """
    db_number = 109
    start = 0
    data = ff
    

    
    wordlen = snap7.snap7types.S7WLReal
    type_ = snap7.snap7types.wordlen_to_ctypes[wordlen]
    size = len(data)
    cdata = (type_ * size).from_buffer(data)
    logger.debug("db_write db_number:%s start:%s size:%s data:%s" %
                 (db_number, start, size, data))
    return self.library.Cli_DBWrite(self.pointer, db_number, start, size,
                                    byref(cdata))

[gijzelaerr]

It looks like that error can't come from the code you copy pasted. Also I get the idea are not really familiar with Python since you try to override the existing client code? I think it is wise to maybe follow some python tutorials.

Try something like this:

import snap 7
client = snap7.client.Client()
client.connect('192.168.5.2', 0, 1)
db_number = 109
start = 0
data = ff
client.db_write(self, db_number, start, data)

hope that gets you a bit further.

[Youandi12]

We have run your program and have the same problems
We don't know what the attributeError is or how we can solve that.

Python 2.7.9 (default, Sep 17 2016, 20:26:04)
[GCC 4.9.2] on linux2
Type "copyright", "credits" or "license()" for more information.

================================ RESTART ================================

Traceback (most recent call last):
File "/home/pi/testcom3.py", line 2, in
client = snap7.client.Client()
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 36, in init
self.create()
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 43, in create
self.library.Cli_Create.restype = c_void_p
AttributeError: 'NoneType' object has no attribute 'Cli_Create'

[gijzelaerr]

you don't get an other error about snap7 library not found? How did you install snap7? Did you modify the python-snap7 source code?

[Youandi12]

These are the only errors we get. Normally the snap7 library is ok.
We have installed the snap7 library with:
$ p7zip -d snap7-full-1.0.0.7z
$ cd build/unix
$ make -f arm_v7_linux.mk
pip install python-snap7

We didn't modify anything in the source code.

[gijzelaerr]

what happens if you run

from ctypes.util import find_library
print find_library('snap7')

in a python console or script?

[Youandi12]

we got this:

libsnap7.so

[gijzelaerr]

And what does this give you:

from ctypes import cdll
from ctypes.util import find_library
print cdll.LoadLibrary(find_library('snap7'))

[Youandi12]

<CDLL 'libsnap7.so', handle 5de320 at 756d0ff0>

[gijzelaerr]

are you sure you didn't modify the client code? This should just work... try uninstalling python-snap7 and reinstalling from pip.

[gijzelaerr]

hm you might have spotted a bug actually.

https://github.com/gijzelaerr/python-snap7/blob/master/snap7/common.py#L42

are you running this in an interactive terminal? it looks like if you called the find_library function before it will return None. Can you restart the interpreter?

[gijzelaerr]

nah that doesn't seem the case.... hm

[Youandi12]

we have changed the common.py en we add the lib_location='/usr/local/lib/libsnap7.so
above return your marked return (boven return heb ik deze regel ingezet )

i have follow this
You will need to edit the lib_location on common.py in the /usr/local/lib/python2.7/dist-packages/snap7/ directory
Add a line in the init part of the Snap7Library class:
lib_location='/usr/local/lib/libsnap7.so'
example below:

class Snap7Library(object):
    """
    Snap7 loader and encapsulator. We make this a singleton to make
    sure the library is loaded only once.
    """
    _instance = None
    def __new__(cls, *args, **kwargs):
        if not cls._instance:
            cls._instance = object.__new__(cls)
            cls._instance.lib_location = None
            cls._instance.cdll = None
        return cls._instance

    def __init__(self, lib_location=None):
        lib_location='/usr/local/lib/libsnap7.so' # add this line here
        if self.cdll:
            return
        self.lib_location = lib_location or self.lib_location or find_library('snap7')
        if not self.lib_location:
            msg = "can't find snap7 library. If installed, try running ldconfig"
            raise Snap7Exception(msg)
        self.cdll = cdll.LoadLibrary(self.lib_location)

[Youandi12]

hi ,
We have reinstalled snap 7 and his library. We tested this like you told us yesterday and it says that the library is installed.
Our faults of yesterday are gone, but we have a new problem if we try this:
import snap 7
client = snap7.client.Client()
client.connect('192.168.5.2', 0, 1)
db_number = 109
start = 0
data = ff
client.db_write(self, db_number, start, data)

We get this fault:
Traceback (most recent call last):
File "/home/pi/TEST3.py", line 8, in
client.db_write(self, db_number, start, data)
NameError: name 'self' is not defined

Could you help us please?

[gijzelaerr]

don't give self to the method. Please google for 'python' and 'self', for example this explains more:

http://stackoverflow.com/questions/7721920/when-do-you-use-self-in-python

import snap 7
client = snap7.client.Client()
client.connect('192.168.5.2', 0, 1)
db_number = 109
start = 0
data = ff
client.db_write(db_number, start, data)

[Youandi12]

if we remove self then we got this problems
Traceback (most recent call last):
File "/home/pi/TEST3.py", line 8, in
client.db_write( db_number, start, data)
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 24, in f
code = func(*args, **kw)
File "/usr/local/lib/python2.7/dist-packages/snap7/client.py", line 152, in db_write
size = len(data)
TypeError: object of type 'int' has no len()

[gijzelaerr]

i'm sorry but you really should get yourself more familiar with Python, otherwise this is going nowhere. Data should be a bytearray.

[Zebrafish007]

It should be data = 'ff' # for all who just new to python.