Python — How do you view output that doesn't fit the screen?

Question

I should say I\'m looking for a solution to the problem of viewing output that does not fit on your screen. For example, range(100) will show the last 30ish lin

Answer 1

There's one fundamental difference between less run in a shell, and Python: Python is a programming language, less is a program.

Bash is aware of what the linecount is in the console, and less can query that (and a number of other things), Python on its own can't be, it's a language and it's agnostic to its environment (that's left to libraries).

On top of that, less obeys some of its own standards. Careted lines get moved to top, it feeds to termcap, it's conceptually part of the OS tools, and it's meant to send to output even if it hasn't finished reading the file.

You can write less in Python if you want, or run it from inside a python script, but its functionality is more (and too specific) than a single method of file should contain.

Answer 2

What have you done when you run into a situation where you wish you could conveniently > scroll through some large output?

1. Don't create large output. Use functions to summarize or show selected details.

2. Simplify the application to avoid creating large output in the first place.

3. Focus what I'm looking at to avoid large output.

4. Generally avoid large output.

It seems simpler to avoid large output than to fuss around trying to display something I never cared about in the first place.

Answer 3

It's easy to write your own:

def less(s, line_count = 5):
    lines = []
    for i, line in enumerate(s.split('\n'), 1):
        lines.append(line)
        if (i % line_count) == 0:
            yield '\n'.join(lines)
            lines = []

    if lines:
        yield '\n'.join(lines)

Answer 4

If you work in ipython you can issue shell commands within your interactive python session. That means that you just do

In [1]: less myfile.txt

I also really like being able to arrow up and down to get previous commands and getting the output from previous commands by doing something like

In [33]: print cos(Out[7]*pi/180)

Answer 5

If you want to do this for an interactive python session, you should use a terminal emulation that allows you to scroll back up. I believe most of them do.

If you're using an actual terminal, or if you don't have a choice of terminal emulators, perhaps you can use GNU screen.

(If you're using Windows, you can change the screen buffer size to allow scrolling back up to 9999 lines).

And if you need this for the output of your program, you can try to use the curses module to implement scrolling yourself.

Answer 6

Yes, there is a way and it is quite trivial, that's why not specifically described. Say you have long list and want to see just the beginning:

>>> lst = range(1000)   # let's make list of thousand elements
>>> lst[:100]           # i want to see just the first 100
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
>>> lst[100:201]        # ok, now the 2nd hundred 
[100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200]
>>> lst[-100:]          # and now just the last 100, pretty please?
[900, 901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911, 912, 913, 914, 915, 916, 917, 918, 919, 920, 921, 922, 923, 924, 925, 926, 927, 928, 929, 930, 931, 932, 933, 934, 935, 936, 937, 938, 939, 940, 941, 942, 943, 944, 945, 946, 947, 948, 949, 950, 951, 952, 953, 954, 955, 956, 957, 958, 959, 960, 961, 962, 963, 964, 965, 966, 967, 968, 969, 970, 971, 972, 973, 974, 975, 976, 977, 978, 979, 980, 981, 982, 983, 984, 985, 986, 987, 988, 989, 990, 991, 992, 993, 994, 995, 996, 997, 998, 999]

The same [] slicing works the same for strings. For dictionary you can cheat somehow, like using str() to convert it to string and then display with the same slicing :-)