nerd-fonts/bin/scripts/name_parser/query_monospace

#!/usr/bin/env python3
# coding=utf8

import sys
import os.path
import fontforge

###### Some helpers (code from font-patcher)

def check_panose_monospaced(font):
    """ Check if the font's Panose flags say it is monospaced """
    # https://forum.high-logic.com/postedfiles/Panose.pdf
    panose = list(font.os2_panose)
    if panose[0] < 2 or panose[0] > 5:
        return -1 # invalid Panose info
    panose_mono = ((panose[0] == 2 and panose[3] == 9) or
                   (panose[0] == 3 and panose[3] == 3))
    return 1 if panose_mono else 0

def is_monospaced(font):
    """ Check if a font is probably monospaced """
    # Some fonts lie (or have not any Panose flag set), spot check monospaced:
    width = -1
    width_mono = True
    for glyph in [ 0x49, 0x4D, 0x57, 0x61, 0x69, 0x2E ]: # wide and slim glyphs 'I', 'M', 'W', 'a', 'i', '.'
        if not glyph in font:
            # A 'strange' font, believe Panose
            return check_panose_monospaced(font) == 1
        # print(" -> {} {}".format(glyph, font[glyph].width))
        if width < 0:
            width = font[glyph].width
            continue
        if font[glyph].width != width:
            # Exception for fonts like Code New Roman Regular or Hermit Light/Bold:
            # Allow small 'i' and dot to be smaller than normal
            # I believe the source fonts are buggy
            if glyph in [ 0x69, 0x2E ]:
                if width > font[glyph].width:
                    continue
                (xmin, _, xmax, _) = font[glyph].boundingBox()
                if width > xmax - xmin:
                    continue
            width_mono = False
            break
    # We believe our own check more then Panose ;-D
    return width_mono

def get_advance_width(font, extended, minimum):
    """ Get the maximum/minimum advance width in the extended(?) range """
    width = 0
    if extended:
        end = 0x17f
    else:
        end = 0x07e
    for glyph in range(0x21, end):
        if not glyph in font:
            continue
        if glyph in range(0x7F, 0xBF):
            continue # ignore special characters like '1/4' etc
        if width == 0:
            width = font[glyph].width
            continue
        if not minimum and width < font[glyph].width:
            width = font[glyph].width
        elif minimum and width > font[glyph].width:
            width = font[glyph].width
    return width


###### Let's go!

if len(sys.argv) < 2:
    print('Usage: {} font_name [font_name ...]\n'.format(sys.argv[0]))
    sys.exit(1)

print('Examining {} font files'.format(len(sys.argv) - 1))


for filename in sys.argv[1:]:
    fullfile = os.path.basename(filename)
    fname = os.path.splitext(fullfile)[0]

    font = fontforge.open(filename, 1)
    width_mono = is_monospaced(font)
    panose_mono = check_panose_monospaced(font)
    if (width_mono and panose_mono == 0) or (not width_mono and panose_mono == 1):
        print('[{:50.50}]  Warning: Monospaced check: Panose assumed to be wrong; Glyph widths {} / {} - {} and Panose says "monospace {}" ({})'.format(fullfile, get_advance_width(font, False, True),
            get_advance_width(font, False, False), get_advance_width(font, True, False), panose_mono, list(font.os2_panose)))
    if not width_mono:
        print('[{:50.50}]  Warning: Sourcefont is not monospaced - forcing to monospace not advisable, results might be useless; Glyph widths {} / {} - {}'.format(fullfile, get_advance_width(font, False, True),
            get_advance_width(font, False, False), get_advance_width(font, True, False), panose_mono, list(font.os2_panose)))
    else:
        print('[{:50.50}]  OK'.format(fullfile))
    font.close()