LESSON 371 OF 410 · PROJECTS: COMMAND-LINE TOOLS

CLI Tool: cat v3 — Show Special Chars (-A) in Python

Practice

Now build the -A flag of the cat tool, as a new function. It makes whitespace visible: every tab character (\t) is replaced by the two characters ^I and every line ends with a literal $ marker (so trailing spaces become obvious). Lines are then joined with newlines.

Note: real cat -A also shows other control characters (such as ^M) and non-ASCII bytes; this version only handles tabs and line ends, like cat -T -E. A blank line becomes just $, and an empty list gives an empty string.

Function signature:

def showAllCat(self, lines: List[str]) -> str:

Example:

Input: lines = ["hello\tworld", "foo"]

Output: "hello^Iworld$\nfoo$"

When printed:
hello^Iworld$
foo$

Another example (a blank line, trailing spaces):

Input: lines = ["a\t", "", "x  "]

Output: "a^I$\n$\nx  $"

When printed:
a^I$
$
x  $

Two transformations per line: replace tabs with "^I", then append "$". After both, join all the transformed lines with "\n".

Python strings have a built-in replace:

line.replace("\t", "^I") + "$"

Append each transformed line to a list, then "\n".join(out).

The full solution:

class Solution:
    def showAllCat(self, lines):
        out = []
        for line in lines:
            out.append(line.replace("\t", "^I") + "$")
        return "\n".join(out)

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CLI Tool: cat v3 — Show Special Chars (-A) in Python

Cat V3 in Python