def bad$\_$visibility$($visibility$,$minimum$)$:

$"""$

Returns True if the visibility measurement violates the minimum, False otherwise

A valid visibility measurement is EITHER the string 'unavailable', or a dictionary

with $($up to$)$ four values: 'minimum', 'maximum', 'prevailing', and 'units'. Only

'prevailing' and 'units' are required; the other two are optional. The units may be

$\text{'}$FT$\text{'}($feet$)$ or $\text{'}$SM$\text{'}$ for $($statute$)$ miles, and explain how to interpret other three

fields, which are all floats.

This function should compare ths visibility 'minimum' $($if it exists$)$ against the

minimum parameter. Else it compares the 'prevailing' visibility. This function returns

True if minimum is more than the measurement. If the visibility is 'unavailable',

then this function returns True $($indicating bad record keeping$).$

Example: Suppose we have the following visibility measurement.

$\{$

"prevailing": $21120\mathrm{.}0,$

"minimum": $1400\mathrm{.}0,$

"maximum": $21120\mathrm{.}0,$

"units": $"$FT$"$

$\}$

Given the above measurement, this function returns True if visibility is $0\mathrm{.}25($miles$)$

and False if it is $1.$

Parameter visibility: The visibility information

Precondition: visibility is a valid visibility measurement, as described above.

$($e$.$g$.$ either a dictionary or the string 'unavailable'$)$

Parameter minimum: The minimum allowed visibility $($in statute miles$)$

Precondition: minimum is a float or int

$"""$

if type$($visibility$)$ is str:

return visibility $==$ 'unavailable'

else:

if "minimum" in visibility:

if visibility$["$units$"]=="$FT$"$:

visibility$["$minimum$"]/=5280$

return minimum $$ visibility$["$minimum$"]$

else:

if visibility$["$units$"]=="$FT$"$:

visibility$["$prevailing$"]/=5280$

return minimum $$ visibility$["$prevailing$"]$