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"""
A collection of utility routines and classes used by the spatial
backends.
"""
def getstatusoutput(cmd):
"""
Executes a shell command on the platform using subprocess.Popen and
return a tuple of the status and stdout output.
"""
from subprocess import Popen, PIPE
# Set stdout and stderr to PIPE because we want to capture stdout and
# prevent stderr from displaying.
p = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE)
# We use p.communicate() instead of p.wait() to avoid deadlocks if the
# output buffers exceed POSIX buffer size.
stdout, stderr = p.communicate()
return p.returncode, stdout.strip()
def gqn(val):
"""
The geographic quote name function; used for quoting tables and
geometries (they use single rather than the double quotes of the
backend quotename function).
"""
if isinstance(val, basestring):
if isinstance(val, unicode): val = val.encode('ascii')
return "'%s'" % val
else:
return str(val)
class SpatialOperation(object):
"""
Base class for generating spatial SQL.
"""
sql_template = '%(geo_col)s %(operator)s %(geometry)s'
def __init__(self, function='', operator='', result='', **kwargs):
self.function = function
self.operator = operator
self.result = result
self.extra = kwargs
def as_sql(self, geo_col, geometry='%s'):
return self.sql_template % self.params(geo_col, geometry)
def params(self, geo_col, geometry):
params = {'function' : self.function,
'geo_col' : geo_col,
'geometry' : geometry,
'operator' : self.operator,
'result' : self.result,
}
params.update(self.extra)
return params
class SpatialFunction(SpatialOperation):
"""
Base class for generating spatial SQL related to a function.
"""
sql_template = '%(function)s(%(geo_col)s, %(geometry)s)'
def __init__(self, func, result='', operator='', **kwargs):
# Getting the function prefix.
default = {'function' : func,
'operator' : operator,
'result' : result
}
kwargs.update(default)
super(SpatialFunction, self).__init__(**kwargs)
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