$4.$ Implement letter$\_$grades

Read the specification of the function letter$\_$grades in the module funcs. Implement this function according to its specification. Once again, the inputs to this function must be dictionaries that have netids as keys and numbers as values. Look at the test cases in tests.py if you are unsure.

When you have implemented the function, test your answer with the test script. You should now pass all tests.

def letter$\_$grades$($adict$)$:

$"""$

Returns a new dictionary with the letter grades for each student.

The dictionary adict has netids for keys and numbers $0-100$ for values. These

represent the grades that the students got on the exam. This function returns a

new dictionary with netids for keys and letter grades $($strings$)$ for values.

Our cut$-$off is $90$ for an A$,80$ for a B$,70$ for a C$,60$ for a D$.$ Anything below $60$

is an F$.$

Examples:

letter$\_$grades$(\{\text{'}$wmw$2\text{'}$ : $55,$ 'abc$3\text{'}$ : $90,\text{'}$jms$45\text{'}$: $86\})$ returns

$\{\text{'}$wmw$2\text{'}$ : $\text{'}$F$,$ 'abc$3\text{'}$ : $\text{'}$A$\text{'},\text{'}$jms$45\text{'}$: $\text{'}$B$\text{'}\}.$

letter$\_$grades$(\{\})$ returns $\{\}$

Parameter adict: the dictionary of grades

Precondition: adict is dictionary mapping strings to ints

$"""$

pass