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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 def __init__(self, function='', operator='', result='', beg_subst='', end_subst=''): |
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37 self.function = function |
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38 self.operator = operator |
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39 self.result = result |
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40 self.beg_subst = beg_subst |
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41 try: |
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42 # Try and put the operator and result into to the |
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43 # end substitution. |
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44 self.end_subst = end_subst % (operator, result) |
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45 except TypeError: |
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46 self.end_subst = end_subst |
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47 |
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48 @property |
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49 def sql_subst(self): |
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50 return ''.join([self.beg_subst, self.end_subst]) |
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51 |
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52 def as_sql(self, geo_col): |
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53 return self.sql_subst % self.params(geo_col) |
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54 |
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55 def params(self, geo_col): |
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56 return (geo_col, self.operator) |
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57 |
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58 class SpatialFunction(SpatialOperation): |
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59 """ |
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60 Base class for generating spatial SQL related to a function. |
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61 """ |
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62 def __init__(self, func, beg_subst='%s(%s, %%s', end_subst=')', result='', operator=''): |
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63 # Getting the function prefix. |
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64 kwargs = {'function' : func, 'operator' : operator, 'result' : result, |
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65 'beg_subst' : beg_subst, 'end_subst' : end_subst,} |
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66 super(SpatialFunction, self).__init__(**kwargs) |
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67 |
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68 def params(self, geo_col): |
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69 return (self.function, geo_col) |