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bpo-32820: Simplify __format__ implementation for ipaddress. #16378

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merged 2 commits into from
Sep 27, 2019
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bpo-32820: Simplify __format__ implementation for ipaddress. #16378

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bpo-32820: Simplify __format__ implementation for ipaddress.
serhiy-storchaka Sep 25, 2019
8376c08
Make __format__ more generic.
serhiy-storchaka Sep 26, 2019
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59 changes: 19 additions & 40 deletions Lib/ipaddress.py
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Original file line number Diff line number Diff line change
Expand Up @@ -560,6 +560,8 @@ def __reduce__(self):
return self.__class__, (str(self),)


_address_fmt_re = None

@functools.total_ordering
class _BaseAddress(_IPAddressBase):

Expand Down Expand Up @@ -623,72 +625,49 @@ def __format__(self, fmt):

Supported presentation types are:
's': returns the IP address as a string (default)
'b' or 'n': converts to binary and returns a zero-padded string
'b': converts to binary and returns a zero-padded string
'X' or 'x': converts to upper- or lower-case hex and returns a zero-padded string
'n': the same as 'b' for IPv4 and 'x' for IPv6

For binary and hex presentation types, the alternate form specifier
'#' and the grouping option '_' are supported.
"""


# Support string formatting
if not fmt or fmt[-1] == 's':
# let format() handle it
return format(str(self), fmt)

# From here on down, support for 'bnXx'
global _address_fmt_re
if _address_fmt_re is None:
import re
_address_fmt_re = re.compile('(#?)(_?)([xbnX])')

import re
fmt_re = '^(?P<alternate>#?)(?P<grouping>_?)(?P<fmt_base>[xbnX]){1}$'
m = re.match(fmt_re, fmt)
m = _address_fmt_re.fullmatch(fmt)
if not m:
return super().__format__(fmt)

groupdict = m.groupdict()
alternate = groupdict['alternate']
grouping = groupdict['grouping']
fmt_base = groupdict['fmt_base']
alternate, grouping, fmt_base = m.groups()

# Set some defaults
if fmt_base == 'n':
if self._version == 4:
fmt_base = 'b' # Binary is default for ipv4
if self._version == 6:
else:
fmt_base = 'x' # Hex is default for ipv6

# Handle binary formatting
if fmt_base == 'b':
if self._version == 4:
# resulting string is '0b' + 32 bits
# plus 7 _ if needed
padlen = IPV4LENGTH+2 + (7*len(grouping))
elif self._version == 6:
# resulting string is '0b' + 128 bits
# plus 31 _ if needed
padlen = IPV6LENGTH+2 + (31*len(grouping))

# Handle hex formatting
elif fmt_base in 'Xx':
if self._version == 4:
# resulting string is '0x' + 8 hex digits
# plus a single _ if needed
padlen = int(IPV4LENGTH/4)+2 + len(grouping)
elif self._version == 6:
# resulting string is '0x' + 32 hex digits
# plus 7 _ if needed
padlen = int(IPV6LENGTH/4)+2 + (7*len(grouping))

retstr = f'{int(self):#0{padlen}{grouping}{fmt_base}}'
padlen = self._max_prefixlen
else:
padlen = self._max_prefixlen // 4

if fmt_base == 'X':
retstr = retstr.upper()
if grouping:
padlen += padlen // 4 - 1

# If alternate is not set, strip the two leftmost
# characters ('0b')
if not alternate:
retstr = retstr[2:]
if alternate:
padlen += 2 # 0b or 0x

return retstr
return format(int(self), f'{alternate}0{padlen}{grouping}{fmt_base}')


@functools.total_ordering
Expand Down