Save data to format csv is not work

PyBaMM Q&A
1

sol.save_data(***,to_format=“csv”) was worked at the previous version, but it is not work after updating to newer version. What am I gonna do?
Here is my code:

%pip install pybamm -q # install PyBaMM if it is not installed
import pybamm
import matplotlib.pyplot as plt
import numpy as np

parameter_values = pybamm.ParameterValues(“OKane2022”)
model = pybamm.lithium_ion.DFN({
“particle mechanics”: “swelling and cracking”,
“SEI”: “solvent-diffusion limited”,
“SEI on cracks”: “true”,
“lithium plating”: “partially reversible”,
})

experiment = pybamm.Experiment([
(f"Discharge at 0.3C until 2.75V",
“Rest for 10 min”,
f"Charge at 0.3C until 4.2V",
f"Hold at 4.2V until C/50")
] * 100,
termination=“80% capacity”
)
sim = pybamm.Simulation(model, experiment=experiment, parameter_values=parameter_values)
sol = sim.solve(save_at_cycles=10)

sol.save_data(“test.csv”, [“Time [h]”, “Current [A]”, “Terminal voltage [V]”], to_format=“csv”)

and the error is:

AttributeError Traceback (most recent call last)
/tmp/ipykernel_4605/3950115692.py in
----> 1 sol.save_data(“test.csv”, [“Time [h]”, “Current [A]”, “Terminal voltage [V]”], to_format=“csv”)

~/anaconda3/lib/python3.9/site-packages/pybamm/solvers/solution.py in save_data(self, filename, variables, to_format, short_names)
673 str if ‘csv’ or ‘json’ is chosen and filename is None, otherwise None
674 “”"
→ 675 data = self.get_data_dict(variables=variables, short_names=short_names)
676
677 if to_format == “pickle”:

~/anaconda3/lib/python3.9/site-packages/pybamm/solvers/solution.py in get_data_dict(self, variables, short_names, cycles_and_steps)
633 for i, cycle in enumerate(self.cycles):
634 data_short_names[“Cycle”] = np.concatenate(
→ 635 [data_short_names[“Cycle”], i * np.ones_like(cycle.t)]
636 )
637 for j, step in enumerate(cycle.steps):

AttributeError: ‘NoneType’ object has no attribute ‘t’

2

It looks like a bug related to save_at_cycles, since some of the cycles are being set to None. You could manually loop over the cycles (for cycle in sol.cycles) and only save the cycles that are not None. Otherwise, implementing your own save to csv is not too difficult, just do this

df = {sol[var].data for var in variables}
df.to_csv("test.csv")