Leo - 8 months ago 19

Python Question

`def get_party_stats(families, table_size=6):`

"""To calculate the number of attendees and tables needed.

Args:

families(list): a list of members.

table_size(int): table size of 6.

Returns:

mixed: people count & table count.

Examples:

>>> get_party_stats([['Jan'], ['Jen', 'Jess'], ['Jem', 'Jack',

'Janis']])

'(6, 3)'

"""

table_num = 0

people_num = 0

for people in families:

table_num += -(-len(people)//table_size)

people_num += len(people)

return people_num, table_num

How do you get

`people_num`

`6`

`len(people)`

`3`

`table_num`

`-(-len(people)//table_size)`

Answer

Since you sum over the sizes of each family `people_num`

will come out as `len(['Jan']) + len(['Jen', 'Jess']) + len(['Jem', 'Jack', 'Janis']) = 1 + 2 + 3 = 6`

.

The `-(-len(people)//table_size)`

term is a bit sneaky but you will realize what it does by noting that `a // b == floor(a / b)`

. Integer division `c = a // b`

is defined such that `c`

is the biggest integer number such that `c <= a / b`

(note that `/`

means float-division here). This makes `abs(a) // abs(b) != abs(a // b)`

when `a / b < 0`

but is exactly what you want when calculating the number of tables necessary in your function.

The following results may illustrate that:

```
-1 // 6 == -1 1 // 6 == 0
-2 // 6 == -1 2 // 6 == 0
... ...
-6 // 6 == -1 6 // 6 == 1
-7 // 6 == -2 7 // 6 == 1
-8 // 6 == -2 8 // 6 == 1
... ...
-12 // 6 == -2 12 // 6 == 2
-13 // 6 == -3 13 // 6 == 2
```

Another (maybe less elegant) way of calculating the number of tables necessary given `people`

would be `1 + (len(people) - 1) // table_size`

.

Finally, the whole function could be made a lot shorter using list-comprehensions:

```
def get_party_stats(families, table_size=6):
return (sum([len(f) for f in families]),
sum([-(-len(f) // table_size) for f in families]))
```