import ctypes
import six
from collections.abc import Sequence
from nidaqmx._lib import lib_importer, ctypes_byte_str
from nidaqmx.errors import (
check_for_error, is_string_buffer_too_small, DaqError)
from nidaqmx.error_codes import DAQmxErrors
from nidaqmx.system.storage.persisted_channel import PersistedChannel
from nidaqmx.utils import unflatten_channel_string
[docs]class PersistedChannelCollection(Sequence):
"""
Contains the collection of global channels for a DAQmx system.
This class defines methods that implements a container object.
"""
def __contains__(self, item):
channel_names = self.global_channel_names
if isinstance(item, six.string_types):
items = unflatten_channel_string(item)
return all([i in channel_names for i in items])
elif isinstance(item, PersistedChannel):
return item._name in channel_names
def __eq__(self, other):
if isinstance(other, self.__class__):
return True
return False
def __getitem__(self, index):
"""
Indexes a subset of global channels on this global channel
collection.
Args:
index: The value of the index. The following index types
are supported:
- str: Name of the global channel. You also can specify
a string that contains a list or range of names to
this input. If you have a list of names, use the
DAQmx Flatten Channel String function to convert
the list to a string.
- int: Index/position of the global channel in the
collection.
- slice: Range of the indexes/positions of global
channels in the collection.
Returns:
List[nidaqmx.system.storage.persisted_channel.PersistedChannel]:
Indicates the of global channels indexed.
"""
if isinstance(index, six.integer_types):
return PersistedChannel(self.global_channel_names[index])
elif isinstance(index, slice):
return [PersistedChannel(name) for name in
self.global_channel_names[index]]
elif isinstance(index, six.string_types):
names = unflatten_channel_string(index)
if len(names) == 1:
return PersistedChannel(names[0])
return [PersistedChannel(name) for name in names]
else:
raise DaqError(
'Invalid index type "{0}" used to access collection.'
.format(type(index)), DAQmxErrors.UNKNOWN)
def __iter__(self):
for channel_name in self.global_channel_names:
yield PersistedChannel(channel_name)
def __len__(self):
return len(self.global_channel_names)
def __ne__(self, other):
return not self.__eq__(other)
def __reversed__(self):
channel_names = self.global_channel_names
channel_names.reverse()
for channel_name in channel_names:
yield PersistedChannel(channel_name)
@property
def global_channel_names(self):
"""
List[str]: The names of all the global channels on this
collection.
"""
cfunc = lib_importer.windll.DAQmxGetSysGlobalChans
if cfunc.argtypes is None:
with cfunc.arglock:
if cfunc.argtypes is None:
cfunc.argtypes = [
ctypes.c_char_p, ctypes.c_uint]
temp_size = 0
while True:
val = ctypes.create_string_buffer(temp_size)
size_or_code = cfunc(
val, temp_size)
if is_string_buffer_too_small(size_or_code):
# Buffer size must have changed between calls; check again.
temp_size = 0
elif size_or_code > 0 and temp_size == 0:
# Buffer size obtained, use to retrieve data.
temp_size = size_or_code
else:
break
check_for_error(size_or_code)
return unflatten_channel_string(val.value.decode('ascii'))