326 lines
7.5 KiB
Markdown
326 lines
7.5 KiB
Markdown
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# 30-seconds-of-python-code
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[](https://github.com/kriadmin/30-seconds-of-python-code/blob/master/LICENSE) [](https://gitter.im/30-seconds-of-python-code/Lobby) [](http://makeapullrequest.com) [](https://travis-ci.org/kriadmin/30-seconds-of-python-code) [](https://insight.io/github.com/kriadmin/30-seconds-of-python-code/tree/master/?source=0) [](https://github.com/Flet/semistandard)
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>Python implementation of 30-seconds-of-code.
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**Note**:- This is in no way affiliated with the original [30-seconds-of-code](https://github.com/Chalarangelo/30-seconds-of-code/).
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### chunk
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Chunks an array into smaller lists of a specified size.
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Uses `range` to create a list of desired size. Then use `map` on this list and fill it with splices of `arr`.
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```python
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from math import ceil
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def chunk(arr, size):
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return list(
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map(lambda x: arr[x * size:x * size + size],
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list(range(0, ceil(len(arr) / size)))))
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```
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``` python
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chunk([1,2,3,4,5],2) # [[1,2],[3,4],5]
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```
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### compact
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Removes falsey values from a list.
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Use `filter()` to filter out falsey values (False, None, 0, and "").
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```python
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def compact(arr):
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return list(filter(lambda x: bool(x), arr))
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```
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``` python
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compact([0, 1, False, 2, '', 3, 'a', 's', 34]); // [ 1, 2, 3, 'a', 's', 34 ]
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```
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### count_occurences
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Counts the occurrences of a value in an list.
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Uses the `reduce` functin from built-in module `functools` to increment a counter each time you encounter the specific value inside the list.
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```python
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def count_occurences(arr, val):
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return reduce(
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(lambda x, y: x + 1 if y == val and type(y) == type(val) else x + 0),
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arr)
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```
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```python
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count_occurrences([1, 1, 2, 1, 2, 3], 1) # 3
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```
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### count_vowels
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Retuns `number` of vowels in provided `string`.
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Use a regular expression to count the number of vowels `(A, E, I, O, U)` in a string.
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```python
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import re
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def count_vowels(str):
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return len(len(re.findall(r'[aeiou]', str, re.IGNORECASE)))
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```
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``` python
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count_vowels('foobar') # 3
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count_vowels('gym') # 0
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```
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### deep_flatten
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Deep flattens a list.
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Use recursion. Use `list.extend()` with an empty array (`result`) and the spread function to flatten a list. Recursively flatten each element that is a list.
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```python
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def spread(arg):
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ret = []
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for i in arg:
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if isinstance(i, list):
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ret.extend(i)
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else:
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ret.append(i)
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return ret
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def deep_flatten(arr):
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result = []
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result.extend(spread(list(map(lambda x : deep(x) if type(x) == list else x,arr))))
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return result
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```
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```python
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deep_flatten([1, [2], [[3], 4], 5]) # [1,2,3,4,5]
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```
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### difference
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Returns the difference between two arrays.
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Create a `set` from `b`, then use list comprehension to only keep values not contained in `b`
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```python
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def difference(a, b):
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b = set(b)
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return [item for item in a if item not in b]
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```
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``` python
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difference([1, 2, 3], [1, 2, 4]) # [3]
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```
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### gcd
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Calculates the greatest common divisor between two or more numbers/lists.
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The `helperGcdfunction` uses recursion. Base case is when `y` equals `0`. In this case, return `x`. Otherwise, return the GCD of `y` and the remainder of the division `x/y`.
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Uses the reduce function from the inbuilt module `functools`. Also defines a method `spread` for javascript like spreading of lists.
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```python
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from functools import reduce
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def spread(arg):
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ret = []
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for i in arg:
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if isinstance(i, list):
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ret.extend(i)
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else:
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ret.append(i)
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return ret
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def gcd(*args):
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numbers = []
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numbers.extend(spread(list(args)))
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def _gcd(x, y):
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return x if not y else gcd(y, x % y)
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return reduce((lambda x, y: _gcd(x, y)), numbers)
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```
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``` python
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gcd(8,36) # 4
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```
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### lcm
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Returns the least common multiple of two or more numbers.
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Use the `greatest common divisor (GCD)` formula and the fact that `lcm(x,y) = x * y / gcd(x,y)` to determine the least common multiple. The GCD formula uses recursion.
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Uses `reduce` function from the inbuilt module `functools`. Also defines a method `spread` for javascript like spreading of lists.
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```python
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from functools import reduce
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def spread(arg):
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ret = []
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for i in arg:
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if isinstance(i, list):
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ret.extend(i)
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else:
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ret.append(i)
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return ret
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def lcm(*args):
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numbers = []
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numbers.extend(spread(list(args)))
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def _gcd(x, y):
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return x if not y else gcd(y, x % y)
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def _lcm(x, y):
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return x * y / _gcd(x, y)
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return reduce((lambda x, y: _lcm(x, y)), numbers)
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```
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``` python
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lcm(12, 7) # 84
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lcm([1, 3, 4], 5) # 60
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```
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### max_n
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Returns the `n` maximum elements from the provided list. If `n` is greater than or equal to the provided list's length, then return the original list(sorted in descending order).
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Use `list.sort()` combined with the `deepcopy` function from the inbuilt `copy` module to create a shallow clone of the list and sort it in ascending order and then use `list.reverse()` reverse it to make it descending order. Use `[:n]` to get the specified number of elements. Omit the second argument, `n`, to get a one-element array
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```python
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from copy import deepcopy
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def max_n(arr, n=1):
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numbers = deepcopy(arr)
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numbers.sort()
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numbers.reverse()
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return numbers[:n]
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```
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```python
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max_n([1, 2, 3]) # [3]
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max_n([1, 2, 3], 2) # [3,2]
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```
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### min_n
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Returns the `n` minimum elements from the provided list. If `n` is greater than or equal to the provided list's length, then return the original list(sorted in ascending order).
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Use `list.sort()` combined with the `deepcopy` function from the inbuilt `copy` module to create a shallow clone of the list and sort it in ascending order. Use `[:n]` to get the specified number of elements. Omit the second argument, `n`, to get a one-element array
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```python
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from copy import deepcopy
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def min_n(arr, n=1):
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numbers = deepcopy(arr)
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numbers.sort()
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return numbers[:n]
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```
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```python
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min_n([1, 2, 3]) # [1]
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min_n([1, 2, 3], 2) # [1,2]
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```
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### shuffle
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Randomizes the order of the values of an list, returning a new list.
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Uses the [Fisher-Yates algorithm](https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle) to reorder the elements of the list.
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```python
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from copy import deepcopy
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from random import randint
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def shuffle(arr):
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temp_arr = deepcopy(arr)
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m = len(temp_arr)
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while(m):
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m -= 1
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i = randint(0, m)
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temp_arr[m], temp_arr[i] = temp_arr[i], temp_arr[m]
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return temp_arr
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```
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``` python
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foo = [1,2,3]
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shuffle(foo) # [2,3,1] , foo = [1,2,3]
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```
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### spread
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Implements javascript's spread syntax as a function. Flattens the list(non-deep) and returns an list.
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```python
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def spread(arg):
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ret = []
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for i in arg:
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if isinstance(i, list):
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ret.extend(i)
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else:
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ret.append(i)
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return ret
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```
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```python
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spread([1,2,3,[4,5,6],[7],8,9]) # [1,2,3,4,5,6,7,8,9]
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```
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## Credits
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*Icons made by [Smashicons](https://www.flaticon.com/authors/smashicons) from [www.flaticon.com](https://www.flaticon.com/) is licensed by [CC 3.0 BY](http://creativecommons.org/licenses/by/3.0/).*
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