So I've written my own model (the details of the model are not important for this question), and the relevant code is

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```
import numpy as np
from .lattice import Lattice, Site, Chain
from ..networks.site import FermionSite
from .model import MultiCouplingModel, CouplingMPOModel
from ..tools.params import get_parameter
from ..tools.misc import any_nonzero
__all__ = ['FQHChain']
class FQHChain(CouplingMPOModel, MultiCouplingModel):
r""" Add details about the model here
"""
def __init__(self, model_params):
CouplingMPOModel.__init__(self, model_params)
def init_sites(self, model_params):
site = FermionSite(conserve='N')
return site
def init_lattice(self, model_params):
site = self.init_sites(model_params)
L = get_parameter(model_params, 'L', 2, self.name) # default values of parameters are currently arbitrary.
bc_MPS = get_parameter(model_params, 'bc_MPS', 'infinite', self.name)
bc = 'periodic' if bc_MPS == 'infinite' else 'open'
lat = Chain(L, site, bc=bc, bc_MPS=bc_MPS)
return lat
def init_terms(self, model_params):
V10 = get_parameter(model_params, 'V10', 1., name, asarray=True) # default values of parameters are currently arbitrary.
V20 = get_parameter(model_params, 'V20', 0.2, name, True)
V21 = get_parameter(model_params, 'V21', 0.5, name, True)
self.add_coupling(V10, 0, 'N', 0, 'N', 1)
self.add_coupling(V20, 0, 'N', 0, 'N', 2)
self.add_multi_coupling(-V21, 0, 'Cd', [(0, 'C', 1), (0, 'C', 2), (0, 'Cd', 3)] )
self.add_multi_coupling(-V21, 0, 'C', [(0, 'Cd', -1), (0, 'Cd', -2), (0, 'C', -3)] ) # h.c. of previous term
# done
```

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```
/Users/username/TeNPy/tenpy/models
```

Code: Select all

```
from tenpy.models.fqh_chain import FQHChain
```

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```
Traceback (most recent call last):
File "fqh_test.py", line 1, in <module>
from tenpy.models.fqh_chain import FQHChain
ModuleNotFoundError: No module named 'tenpy.models.fqh_chain'
```

Code: Select all

```
from tenpy.models.toric_code import ToricCode
```

Does anybody know why this happens?

I am new to python 3, this is the first time I'm using it.