I'm writing a function that is supposed to decode an inputted NRZ scheme. My professor also prohibited any usages of import libraries. Here's my code so far.

def nrz_encoding(input_scheme):
    # Split the input into lines and convert each line into a list of characters
    nrz_scheme = [list(line) for line in input_scheme.strip().split('\n')]

    index = 0
    nrz_output = ''

    # Identify the first and last rows
    first_row = nrz_scheme[0]
    last_row = nrz_scheme[3]

    # Determine the starting row (first or last) based on the leftmost underscore
    if first_row[0] == "_":
       current_row = first_row
    elif last_row[0] == "_":
       current_row = last_row
    else:
        raise ValueError("Please make sure that there's no spaces at the start of your leftmost underscore(_).")

    # Determine the maximum length of the rows
    max_length = max(len(first_row), len(last_row))

    while index < max_length:
        # Determine the current row based on the signal level
        if index < len(first_row) and first_row[index] == "_":
            current_row = first_row
        elif index < len(last_row) and last_row[index] == "_":
            current_row = last_row

        # Translate the signal level to 0 or 1
        if current_row is first_row:
            nrz_output += "0"
        else:
            nrz_output += "1"

        index += 3

        # Check for a transition (vertical bar)
        if index < len(nrz_scheme[1]) and nrz_scheme[1][index] == "|":
            # Switch the current row
            if current_row is first_row:
                current_row = last_row
            else:
                current_row = first_row
            # Move past the transition character
            index += 1

    return nrz_output

I don't know why but it works for some test cases but not others. Like this one:

nrz_input = """
    ______
   |      |
   |      |
___|      |___
"""

The input above should spit out a 0110 based on the scheme. But my code outputs a 1000. I don't really know why either. Also, I should note that I'm fairly new to coding.

I'm writing a function that is supposed to decode an inputted NRZ scheme. My professor also prohibited any usages of import libraries. Here's my code so far.

def nrz_encoding(input_scheme):
    # Split the input into lines and convert each line into a list of characters
    nrz_scheme = [list(line) for line in input_scheme.strip().split('\n')]

    index = 0
    nrz_output = ''

    # Identify the first and last rows
    first_row = nrz_scheme[0]
    last_row = nrz_scheme[3]

    # Determine the starting row (first or last) based on the leftmost underscore
    if first_row[0] == "_":
       current_row = first_row
    elif last_row[0] == "_":
       current_row = last_row
    else:
        raise ValueError("Please make sure that there's no spaces at the start of your leftmost underscore(_).")

    # Determine the maximum length of the rows
    max_length = max(len(first_row), len(last_row))

    while index < max_length:
        # Determine the current row based on the signal level
        if index < len(first_row) and first_row[index] == "_":
            current_row = first_row
        elif index < len(last_row) and last_row[index] == "_":
            current_row = last_row

        # Translate the signal level to 0 or 1
        if current_row is first_row:
            nrz_output += "0"
        else:
            nrz_output += "1"

        index += 3

        # Check for a transition (vertical bar)
        if index < len(nrz_scheme[1]) and nrz_scheme[1][index] == "|":
            # Switch the current row
            if current_row is first_row:
                current_row = last_row
            else:
                current_row = first_row
            # Move past the transition character
            index += 1

    return nrz_output

I don't know why but it works for some test cases but not others. Like this one:

nrz_input = """
    ______
   |      |
   |      |
___|      |___
"""

The input above should spit out a 0110 based on the scheme. But my code outputs a 1000. I don't really know why either. Also, I should note that I'm fairly new to coding.

• python

Share Improve this question Follow edited Mar 4 at 1:40 Tuan Nguyen asked Mar 4 at 1:35 Tuan NguyenTuan Nguyen 122 bronze badges

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1 Answer 1

Sorted by: Reset to default 0

You have two major problems.

First, you do input_scheme.strip(). That gets rid of the leading spaces in your first line. If you had done print(first_line) and print(last_line), you would have seen that.

Once you do that, you have a problem because there's a blank first line. You can resolve that by deleting the first (empty) line.

(Note that you don't need to convert each line to a list. Since you aren't changing them, a string operates exactly like a list in this case.)

Finally, you have the levels swapped. If your match is in the first row, then the level is 1, not 0.

So, if I make these two changes:

    nrz_scheme = input_scheme.splitlines()[1:]

and

        # Translate the signal level to 0 or 1
        if current_row is first_row:
            nrz_output += "1"
        else:
            nrz_output += "0"

then I get "0110" as an output.

Also, note that you don't need to set the current row BOTH based on the top/bottom AND based on the transition character. You can delete the "# Switch the current_row" block.

So, here's the corrected code:

def nrz_encoding(input_scheme):
    nrz_scheme = input_scheme.splitlines()[1:]

    index = 0
    nrz_output = ''

    # Identify the first and last rows
    first_row = nrz_scheme[0]
    last_row = nrz_scheme[3]

    # Determine the starting row (first or last) based on the leftmost underscore
    if first_row[0] == "_":
       current_row = first_row
    elif last_row[0] == "_":
       current_row = last_row
    else:
        raise ValueError("Please make sure that there's no spaces at the start of your leftmost underscore(_).")

    # Determine the maximum length of the rows
    max_length = max(len(first_row), len(last_row))

    while index < max_length:
        # Determine the current row based on the signal level
        if index < len(first_row) and first_row[index] == "_":
            current_row = first_row
        elif index < len(last_row) and last_row[index] == "_":
            current_row = last_row

        # Translate the signal level to 0 or 1
        if current_row is first_row:
            nrz_output += "1"
        else:
            nrz_output += "0"

        index += 3

        # Check for a transition (vertical bar)
        if index < len(nrz_scheme[1]) and nrz_scheme[1][index] == "|":
            # Move past the transition character
            index += 1

    return nrz_output

nrz_input = """
    ______
   |      |
   |      |
___|      |___
"""

print(nrz_encoding(nrz_input))

And the output:

timr@Tims-NUC:~/src$ python x.py
0110
timr@Tims-NUC:~/src$