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