Question

I’m having problems with a homework question.

“Write a function, to_str(a), that takes an array, a, converts each of
its elements to a string (using str(a[i])) and appends all these
strings together.”

This is what I have

def to_str(a):
    for i in a: a.append([i])
    return str(a[i])

I have no idea how to use str(a[i]), I was wondering if someone can point me to the right direction

Answer 1

From the docs:

str(object) -> string

Return a nice string representation of the object. If the argument is
a string, the return value is the same object.

So str(a[i]) will return a string representation of a[i], i.e. convert a[i] to a string.
You will then need to concatenates the strings for all values of i.

As for your code, I have the following comments:

• i is an element of a, not an index, as you might be thinking;
• you are appending elements of a to a (endlessly, I’m afraid);
• a[i] can cause an exception, because, like I said, i is an element, not an index;
• you need to return a concatenation of strings, not a string from one element.

Also, if using str(a[i]) is not strictly mandatory, I’d suggest to skip it as unpythonic. You don’t need indexes at all for this. Examples:

''.join(str(element) for element in a)

or

''.join(map(str, a))

will return what you need. In both cases str is applied to all elements of a.

The simplest-to-understand (“beginner”) way without using indexes will be

s = ''
for element in a:
    s += str(element)
return s

It’s a bit less efficient, though it does effectively the same thing.