How to use the fontbakery.callable.condition function in fontbakery

@condition
def descfile(family_directory):
  """Get the path of the DESCRIPTION file of a given font project."""
  if family_directory:
    descfilepath = os.path.join(family_directory, "DESCRIPTION.en_us.html")
    if os.path.exists(descfilepath):
      return descfilepath

@condition
def api_gfonts_ttFont(style, remote_styles):
  """Get a TTFont object of a font downloaded from Google Fonts
     corresponding to the given TTFont object of
     a local font being checked.
  """
  if remote_styles and style in remote_styles:
    return remote_styles[style]

@condition
def stylenames_are_canonical(fonts):
  """ Are all font files named canonically ? """
  for font in fonts:
    if not canonical_stylename(font):
      return False
  # otherwise:
  return True

@condition
def expected_os2_weight(style):
  """The weight name and the expected OS/2 usWeightClass value inferred from
  the style part of the font name

  The Google Font's API which serves the fonts can only serve
  the following weights values with the corresponding subfamily styles:

  250, Thin
  275, ExtraLight
  300, Light
  400, Regular
  500, Medium
  600, SemiBold
  700, Bold
  800, ExtraBold
  900, Black

@condition
def familyname_with_spaces(familyname):
  FAMILY_WITH_SPACES_EXCEPTIONS = {'VT323': 'VT323',
                                   'K2D': 'K2D',
                                   'PressStart2P': 'Press Start 2P',
                                   'ABeeZee': 'ABeeZee',
                                   'IBMPlexMono': 'IBM Plex Mono',
                                   'IBMPlexSans': 'IBM Plex Sans',
                                   'IBMPlexSerif': 'IBM Plex Serif'}
  if not familyname:
    return None

  if familyname in FAMILY_WITH_SPACES_EXCEPTIONS.keys():
    return FAMILY_WITH_SPACES_EXCEPTIONS[familyname]

  result = []
  for c in familyname:

@condition
def familyname_with_spaces(familyname):
  FAMILY_WITH_SPACES_EXCEPTIONS = {'VT323': 'VT323',
                                   'K2D': 'K2D',
                                   'PressStart2P': 'Press Start 2P',
                                   'ABeeZee': 'ABeeZee',
                                   'IBMPlexMono': 'IBM Plex Mono',
                                   'IBMPlexSans': 'IBM Plex Sans',
                                   'IBMPlexSerif': 'IBM Plex Serif'}
  if not familyname:
    return None

  if familyname in FAMILY_WITH_SPACES_EXCEPTIONS.keys():
    return FAMILY_WITH_SPACES_EXCEPTIONS[familyname]

  result = []
  for c in familyname:

@condition
def VTT_hinted(ttFont):
  # it seems that VTT is the only program that generates a TSI5 table
  return 'TSI5' in ttFont

@condition
def is_variable_font(ttFont):
  return "fvar" in ttFont.keys()

@condition
def whitelist_librebarcode(font):
  font_filenames = [
    "LibreBarcode39-Regular.ttf",
    "LibreBarcode39Text-Regular.ttf",
    "LibreBarcode128-Regular.ttf",
    "LibreBarcode128Text-Regular.ttf"
  ]
  for font_filename in font_filenames:
    if font_filename in font:
      return True

@condition
def font_metadata(family_metadata, font):
  if not family_metadata:
    return

  for f in family_metadata.fonts:
    if font.endswith(f.filename):
      return f