Why Does .join() Insert Characters Between Elements Instead of Appending a String in Python?

Understanding the Join() Method for String Concatenation

While working with Python, you may come across the notion that .join() is the preferred method for concatenating strings. However, its functionality can be confusing for beginners.

Consider this code snippet:

strid = repr(595)
print(array.array('c', random.sample(string.ascii_letters, 20 - len(strid))).tostring().join(strid))

This code does not behave as expected. Instead of appending "595" to the result, it produces an output of characters from the ASCII alphabet interspersed with the digits of "595."

The .join() Method

To understand why, let's dismantle the .join() method. It takes a string as an argument and inserts it between the elements of a given list. For example:

","join(["a", "b", "c"])

Will produce "a,b,c." The "," is inserted between each element of the list.

In your code, "595" is treated as a list of three individual characters: ["5", "9", "5"]. Consequently, the string argument of the .join() method is inserted between these characters, resulting in the observed output.

Alternative Method:

If your intention is to concatenate the string "595" to the generated string, you should use the operator instead:

print(array.array('c', random.sample(string.ascii_letters, 20 - len(strid))).tostring() + strid)

This will correctly concatenate the two strings, producing a single string with the desired content.

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