my-first-blog/myvenv/Lib/site-packages/django/contrib/gis/gdal/libgdal.py

import logging
import os
import re
from ctypes import CDLL, CFUNCTYPE, c_char_p, c_int
from ctypes.util import find_library

from django.contrib.gis.gdal.error import GDALException
from django.core.exceptions import ImproperlyConfigured

logger = logging.getLogger('django.contrib.gis')

# Custom library path set?
try:
    from django.conf import settings
    lib_path = settings.GDAL_LIBRARY_PATH
except (AttributeError, EnvironmentError,
        ImportError, ImproperlyConfigured):
    lib_path = None

if lib_path:
    lib_names = None
elif os.name == 'nt':
    # Windows NT shared libraries
    lib_names = ['gdal203', 'gdal202', 'gdal201', 'gdal20', 'gdal111']
elif os.name == 'posix':
    # *NIX library names.
    lib_names = ['gdal', 'GDAL', 'gdal2.3.0', 'gdal2.2.0', 'gdal2.1.0', 'gdal2.0.0', 'gdal1.11.0']
else:
    raise ImproperlyConfigured('GDAL is unsupported on OS "%s".' % os.name)

# Using the ctypes `find_library` utility  to find the
# path to the GDAL library from the list of library names.
if lib_names:
    for lib_name in lib_names:
        lib_path = find_library(lib_name)
        if lib_path is not None:
            break

if lib_path is None:
    raise ImproperlyConfigured(
        'Could not find the GDAL library (tried "%s"). Is GDAL installed? '
        'If it is, try setting GDAL_LIBRARY_PATH in your settings.'
        % '", "'.join(lib_names)
    )

# This loads the GDAL/OGR C library
lgdal = CDLL(lib_path)

# On Windows, the GDAL binaries have some OSR routines exported with
# STDCALL, while others are not.  Thus, the library will also need to
# be loaded up as WinDLL for said OSR functions that require the
# different calling convention.
if os.name == 'nt':
    from ctypes import WinDLL
    lwingdal = WinDLL(lib_path)


def std_call(func):
    """
    Return the correct STDCALL function for certain OSR routines on Win32
    platforms.
    """
    if os.name == 'nt':
        return lwingdal[func]
    else:
        return lgdal[func]


# #### Version-information functions. ####

# Return GDAL library version information with the given key.
_version_info = std_call('GDALVersionInfo')
_version_info.argtypes = [c_char_p]
_version_info.restype = c_char_p


def gdal_version():
    "Return only the GDAL version number information."
    return _version_info(b'RELEASE_NAME')


def gdal_full_version():
    "Return the full GDAL version information."
    return _version_info('')


version_regex = re.compile(r'^(?P<major>\d+)\.(?P<minor>\d+)(\.(?P<subminor>\d+))?')


def gdal_version_info():
    ver = gdal_version().decode()
    m = version_regex.match(ver)
    if not m:
        raise GDALException('Could not parse GDAL version string "%s"' % ver)
    return {key: m.group(key) for key in ('major', 'minor', 'subminor')}


_verinfo = gdal_version_info()
GDAL_MAJOR_VERSION = int(_verinfo['major'])
GDAL_MINOR_VERSION = int(_verinfo['minor'])
GDAL_SUBMINOR_VERSION = _verinfo['subminor'] and int(_verinfo['subminor'])
GDAL_VERSION = (GDAL_MAJOR_VERSION, GDAL_MINOR_VERSION, GDAL_SUBMINOR_VERSION)
del _verinfo

# Set library error handling so as errors are logged
CPLErrorHandler = CFUNCTYPE(None, c_int, c_int, c_char_p)


def err_handler(error_class, error_number, message):
    logger.error('GDAL_ERROR %d: %s', error_number, message)


err_handler = CPLErrorHandler(err_handler)


def function(name, args, restype):
    func = std_call(name)
    func.argtypes = args
    func.restype = restype
    return func


set_error_handler = function('CPLSetErrorHandler', [CPLErrorHandler], CPLErrorHandler)
set_error_handler(err_handler)