closes #283

This is a workaround for
kwant/kwant#280
and should be reviewed once that issue has been dealt with.

In order not to complicate the licensing situation of Kwant proper,
the new logo will be maintained in a separate repository.

This is a partial application of the changeset proposed in
kwant/kwant!274,
which removes the need for a 'conftest.py', instead using
'pytest.importorskip'.

We apply this change only to 'qsymm', as applying this change elsewhere
requires rethinking where tests are put in the package structure of
Kwant. This minimal change allows us to build packages for Conda and
Debian, which is necessary for releasing Kwant 1.4.

This allows subclassing of operators by third party libraries
(e.g. tkwant).

This shouldn't be a problem, but sphinx complains.

'temp' is too short a parameter name, especially for an API,
and could be confused with 'temporary'.

Deprecate 'args' parameter in favor of 'params'

Closes #272

See merge request kwant/kwant!280

Some tests are explicitly checking the use of 'args'
against the use of 'params', so these we leave in and
instead suppress the warnings.

Additionally update all associated docstrings to say that 'args'
is deprecated in favor of 'params'.

Also implement a specialization of this decorator for the 'args'
parameter, so as to avoid boilerplate (i.e. redefining the help
string everywhere the decorator is used).

The deprecation decorator can also be called directly with no
parameters to raise the warning. This is necessary because
methods of Cython cdef classes do not seem to play well with
this decorator (even after applying @cython.bind(True)), so
we need to call it directly from the body of the method.

Christoph Groth authored 6 years ago and Joseph Weston committed 6 years ago

This allows third party modules to subclass Kwant's cdef classes.
https://cython.readthedocs.io/en/latest/src/userguide/sharing_declarations.html#search-paths-for-definition-files

This means we don't need to create a dummy class that implements
__get__ just so we can use hamiltonian_submatrix as a method.

Closes #270.

add 'parameters' property to finalized systems, and use this
new API to check when users forget parameters.

See merge request kwant/kwant!275

Also require that 'leads' of FiniteSystems have a 'parameters'
property.

Specifically: finalized Builder, PrecalculatedLead,
              ModesLead and SelfEnergyLead

This can be used to inspect the parameters on which a system depends,
and can be later used to give more informative error messages.

Adding 'parameters' to ModesLead and SelfEnergyLead is strictly a
backwards-incompatible change, however this is an advanced feature of
Kwant and we don't want to let this block adding 'parameters' to the
system API.

Closes #263.

Anton Akhmerov authored 6 years ago and Joseph Weston committed 6 years ago

Also correctly select random sites without repetitions.
Closes issue #265.

This was committed by mistake during debugging.