columns using string formatting python

Question

I'm trying to replicate the ls function in bash with columns like this:

I tried .format to add padding to the file names but im still not getting the desired output the last column overflows everytime.

def show_dirs():
    filelist = os.listdir(os.getcwd())
    filelist.sort()

    scr_width = int(os.popen("stty size", "r").read().split()[1])
    max_len = -1
    for file_len in filelist:
        if len(file_len) > max_len and scr_width > max_len*2:
            max_len = len(file_len)
            mlen = max_len #+ 1

    print(color["cyan"] + "Files in the current directory")

    if scr_width < mlen:
        mlen = scr_width

    line = ""
    for count, _file in enumerate(filelist):
        if os.path.isdir(_file):
            _file = _file + os.sep
            st = "[{0:>2}] {1:<{mlen}}".format(str(count + 1), _file, mlen=mlen)
            if len(line) % scr_width > len(st):
                line = line + color["green"] + st
            else:
                line = line + "\n" + color["green"] + st
        else:
            st = "[{0:>2}] {1:<{mlen}}".format(str(count + 1), _file, mlen=mlen)
            if len(line) % scr_width > len(st):
                line = line + color["cyan"] + st
            else:
                line = line + "\n" + color["cyan"] + st
    print(line)

I get this output:

I find this question to be interesting. Other than brute force, I cannot think of a good method for determining how many columns of text can ft across a screen of a given width. Even determining an upper bound on this number is tough, because a list of inputs may exist that would not fit in N columns, but would in N+1. — Amitai Irron
– Amitai Irron, Commented May 13, 2020 at 19:27

Amitai Irron · Accepted Answer · 2020-05-13 19:38:19Z

1

So, it turns out that column output of a list of arbitrary strings is done by the Linux column command. One option is to assume the existence of this command on your system (it exists in my environment) and to use it as an out-of-process output filter.

Another option is to dig deeper into the source code of columns, and reimplement it in Python, possibly as a generator function. I found a pointer in GitHub. Note that this is over 800 lines of C code.

You can also create Python binding for the core functionality of that C code, which would yield a better performing code. Sadly I do not have experience with integrating C code into Python.

If you decide to opt for the second alternative, you can post your implementation as an answer here.

answered May 13, 2020 at 19:38

Amitai Irron

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3 Comments

Aakash Singh Over a year ago

i looked into the source code of column command but it was too complex

Aakash Singh Over a year ago

I came up with a solution but it only works if the terminal size dosen't change so I am thinking of making a function to refresh the screen with the new columns if the terminal size is changed

Amitai Irron Over a year ago

@AakashSingh - do not that your algorithm uses a fixed column width (I state this based on you output), while the Linux columns (or ls) algorithm only uses columns as wide as the widest element in the column. So, what you are implementing is not what you stated you wanted.

Aakash Singh · Accepted Answer · 2020-05-16 10:51:51Z

I improved my algorithm and now it works fine when the terminal size is fixed

color = {
    "red": "\033[31m",
    "green": "\033[32m",
    "orange": "\033[33m",
    "purple": "\033[35m",
    "cyan": "\033[36m",
    "yellow": "\033[93m",
}


def show_dirs(path=os.getcwd()):
    print(color["cyan"] + "Files in the current directory")
    filelist = os.listdir(path)
    filelist.sort()

    #index padding
    ind = len(filelist)
    if ind >= 1000:
        ind = 4
    elif ind >= 100:
        ind = 3
    elif ind >= 10:
        ind = 2
    else:
        ind = 1

    scr_width = int(os.get_terminal_size()[0]) #terminal width
    mlen = max(len(word) for word in filelist) + 1 #column width
    cols = scr_width // mlen #possible columns

    if scr_width < mlen:
        mlen = scr_width

    line = ""
    lst = []
    for count, _file in enumerate(filelist, start=1):
        if os.path.isdir(_file):
            _file = _file + os.sep
            st = "[{0:>{ind}}] {1:<{mlen}}".format(
                str(count), _file, mlen=mlen, ind=ind
            )
            if scr_width - ((len(line) - cols * 5) % scr_width) > len(st): # - cols * 5 to compensate the length of color codes
                line = line + color["cyan"] + st
            else:
                lst.append(line)
                line = color["cyan"] + st

        else:
            st = "[{0:>{ind}}] {1:<{mlen}}".format(
                str(count), _file, mlen=mlen, ind=ind
            )
            if scr_width - ((len(line) - cols * 5) % scr_width) > len(st): # - cols * 5 to compensate the length of color codes
                line = line + color["green"] + st
            else:
                lst.append(line)
                line = color["green"] + st
    if lst == []:
        lst.append(line)
    print("\n".join(lst))

output:

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