# Python: Symmetric difference between two lists, after applying the provided function to each list element of both

## Python List: Exercise - 227 with Solution

Write a Python program to get the symmetric difference between two lists, after applying the provided function to each list element of both.

- Create a set by applying fn to each element in every list.
- Use a list comprehension in combination with fn on each of them to only keep values not contained in the previously created set of the other.

**Sample Solution:**

**Python Code:**

```
def symmetric_difference_by(a, b, fn):
(_a, _b) = (set(map(fn, a)), set(map(fn, b)))
return [item for item in a if fn(item) not in _b] + [item
for item in b if fn(item) not in _a]
from math import floor
print(symmetric_difference_by([2.1, 1.2], [2.3, 3.4], floor))
```

Sample Output:

[1.2, 3.4]

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**Previous:** Write a Python program to get a list of elements that exist in both lists, after applying the provided function to each list element of both.

**Next:** Write a Python program to get every element that exists in any of the two given lists once, after applying the provided function to each element of both.

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## Python: Tips of the Day

**Floor Division:**

When we speak of division we normally mean (/) float division operator, this will give a precise result in float format with decimals.

For a rounded integer result there is (//) floor division operator in Python. Floor division will only give integer results that are round numbers.

print(1000 // 300) print(1000 / 300)

Output:

3 3.3333333333333335

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