I have below code with an inner function, but it is not returning the "sorted_rsq" whenever I run it with arguments.

```
def improve_model (formula, covariates, data):
"""Returns a new formula which has a new added covariate which is the best single covariate in terms of R^2"""
#Get the formulas given all covariates
olsformulas = extend_model(formula,covariates)
#Using all formulas to calculate R^2 for each
def ols(formula, data):
"""Calculates the R^2 of a given formula."""
all = {}
for formula in olsformulas:
fit = smf.ols(formula,data).fit().rsquared
all[formula] = fit
sorted_rsq = sorted(all.items(), key = lambda x: x[1], reverse = True)
return sorted_rsq[0]
ols(formula,data)
```

Just giving me blank result. Can anyone help me what is wrong with the code?

### >Solution :

Replace `ols(formula,data)`

with `return ols(formula,data)`

at the end of the outer function.