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1 """ |
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2 A collection of utility routines and classes used by the spatial |
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3 backends. |
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4 """ |
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5 |
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6 def getstatusoutput(cmd): |
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7 """ |
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8 Executes a shell command on the platform using subprocess.Popen and |
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9 return a tuple of the status and stdout output. |
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10 """ |
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11 from subprocess import Popen, PIPE |
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12 # Set stdout and stderr to PIPE because we want to capture stdout and |
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13 # prevent stderr from displaying. |
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14 p = Popen(cmd, shell=True, stdout=PIPE, stderr=PIPE) |
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15 # We use p.communicate() instead of p.wait() to avoid deadlocks if the |
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16 # output buffers exceed POSIX buffer size. |
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17 stdout, stderr = p.communicate() |
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18 return p.returncode, stdout.strip() |
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19 |
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20 def gqn(val): |
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21 """ |
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22 The geographic quote name function; used for quoting tables and |
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23 geometries (they use single rather than the double quotes of the |
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24 backend quotename function). |
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25 """ |
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26 if isinstance(val, basestring): |
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27 if isinstance(val, unicode): val = val.encode('ascii') |
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28 return "'%s'" % val |
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29 else: |
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30 return str(val) |
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31 |
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32 class SpatialOperation(object): |
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33 """ |
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34 Base class for generating spatial SQL. |
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35 """ |
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36 sql_template = '%(geo_col)s %(operator)s %(geometry)s' |
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37 |
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38 def __init__(self, function='', operator='', result='', **kwargs): |
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39 self.function = function |
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40 self.operator = operator |
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41 self.result = result |
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42 self.extra = kwargs |
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43 |
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44 def as_sql(self, geo_col, geometry='%s'): |
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45 return self.sql_template % self.params(geo_col, geometry) |
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46 |
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47 def params(self, geo_col, geometry): |
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48 params = {'function' : self.function, |
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49 'geo_col' : geo_col, |
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50 'geometry' : geometry, |
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51 'operator' : self.operator, |
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52 'result' : self.result, |
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53 } |
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54 params.update(self.extra) |
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55 return params |
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56 |
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57 class SpatialFunction(SpatialOperation): |
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58 """ |
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59 Base class for generating spatial SQL related to a function. |
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60 """ |
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61 sql_template = '%(function)s(%(geo_col)s, %(geometry)s)' |
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62 |
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63 def __init__(self, func, result='', operator='', **kwargs): |
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64 # Getting the function prefix. |
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65 default = {'function' : func, |
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66 'operator' : operator, |
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67 'result' : result |
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68 } |
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69 kwargs.update(default) |
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70 super(SpatialFunction, self).__init__(**kwargs) |