Equivalent of java arrays.copyOf() in python

Question

I have to translate a java lib into a python one.

During that process i came across the arrays.copyOf() function (the one for bytes not string).

From Docs:

public static byte[] copyOf(byte[] original, int newLength)
Returns: a copy of the original array, truncated or padded with zeros to obtain the specified length

I would like to know if there is a built in equivalent of it or if there is a lib that does it.

my_data[some_int:some_int] is the equivalent of java copyOfRange() Here I need to output specific length bytes or byte array that will be padded with 0 if too short

Hey @Bastien B, is this what you are looking for? geeksforgeeks.org/python-list-copy-method — Rutangaba
– Rutangaba, Commented Nov 19, 2021 at 14:29
@VictorSaraivaRocha array.copyOf has 2 arguments. The second argument specifies the length of the new array. — Ch3steR
– Ch3steR, Commented Nov 19, 2021 at 14:34
@Bastien I have edited your question. Feel free to revert the changes if not ok. — Ch3steR
– Ch3steR, Commented Nov 19, 2021 at 14:53

Ch3steR · Accepted Answer · 2021-11-19 14:43:27Z

3

We can do this in two steps,

Create a copy of the given list.
We can use slice assignment to return a list of size specified by the second arg.

def copy_of(lst, length):
    out = lst.copy() # This is a shallow copy. 
                     # For deepcopy use `copy.deepcopy(lst)`
    out[length:] = [0 for _ in range(length - len(lst))]
    return out

l = [1, 2, 3]
print(copy_of(l, 5))
# [1, 2, 3, 0, 0]

print(copy_of(l, 2))
# [1, 2]

answered Nov 19, 2021 at 14:43

Ch3steR

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1 Comment

Bastien B Over a year ago

thank you @Ch3steR, i ended up using it with a bytearray lst and it worked like a charm :D

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