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from typing import List

def allocation_num(number_of_bytes: int, partitions: int) -> List[str]:

"""

Divide a number of bytes into x partitions.

In a multi-threaded download, this algorithm could be used to provide

each worker thread with a block of non-overlapping bytes to download.

For example:

for i in allocation_list:

requests.get(url,headers={'Range':f'bytes={i}'})

parameter

------------

: param number_of_bytes

: param partitions

return

------------

: return: list of bytes to be assigned to each worker thread

Examples:

------------

>>> allocation_num(16647, 4)

['0-4161', '4162-8322', '8323-12483', '12484-16647']

>>> allocation_num(888, 888)

Traceback (most recent call last):

...

ValueError: partitions can not >= number_of_bytes!

>>> allocation_num(888, 999)

Traceback (most recent call last):

...

ValueError: partitions can not >= number_of_bytes!

>>> allocation_num(888, -4)

Traceback (most recent call last):

...

ValueError: partitions must be a positive number!

"""

if partitions <= 0:

raise ValueError("partitions must be a positive number!")

if partitions >= number_of_bytes:

raise ValueError("partitions can not >= number_of_bytes!")

bytes_per_partition = number_of_bytes // partitions

allocation_list = [f"0-{bytes_per_partition}"]

for i in range(1, partitions - 1):

length = f"{bytes_per_partition * i + 1}-{bytes_per_partition * (i + 1)}"

allocation_list.append(length)

allocation_list.append(

f"{(bytes_per_partition * (partitions - 1)) + 1}-" f"{number_of_bytes}"

)

return allocation_list

if __name__ == "__main__":

import doctest

doctest.testmod()

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