以根据值具有不同格式的格式化方式打印值？

Question

I'm still relatively new to python and was just wondering how to print values from a function that takes in a list as input and prints every value with a comma separated by every two values except -1 which it just prints by itself (assuming there will always be two values matched together if its not -1).

Some examples would be: input: [2,3,4,2,-1,4,3] output: 2 3, 4 2, -1, 4 3

input: [2,1,-1] output: 2 1, -1

Every time a solution it feels like I'm overthinking it with while loops and if statements. Is there anyway for this to be faster and easier?

Answer 1

For situations where you may need to take multiple elements from a list in one iteration, an iterator is often a viable solution. Calling the built-in iter() on any iterable object (lists, strings, dicts, generators) will provide an iterator, which returns objects one at a time, dynamically, and which cannot backtrack . If you then assign an iterator to a variable and use that variable in a for loop, you can selectively call next() on it yourself to make the loop 'skip' elements:

inp = [2,3,4,2,-1,4,3]
inp_iter = iter(inp)
output = []
for elem in inp_iter:  # each iteration essentially calls next() on the iterator until there is no more next()
    if elem == -1:
        output.append(str(elem))
    else:
        # withdraw the next element from the iterator before the `for` loop does automatically
        # thus, the for loop will skip this element
        next_elem = next(inp_iter)
        output.append(f"{elem} {next_elem}")
print(', '.join(output))
# '2 3, 4 2, -1, 4 3'

You'll need to add error handling to this to deal with edge cases, but this should handle your immediate problem.