src/oscopy/writers/writer.py

   1 """ Common signal export functions
   2 """
   3
   4 import os.path
   5
   6 class WriteError(Exception):
   7     """
   8 Class WriteError -- Errors encountered when writing file
   9 methods:
  10     __init__(value)
  11       Assign the error message
  12
  13     __str__()
  14       Return a string with the error message
  15     """
  16     def __init__(self, msg):
  17         """ Assign the error message
  18
  19         Parameter
  20         ---------
  21         msg: string
  22         The error message
  23
  24         Returns
  25         -------
  26         WriteError
  27         The object instanciated
  28         """
  29         self._msg = msg
  30
  31     def __str__(self):
  32         """ Returns the error message
  33
  34         Parameter
  35         ---------
  36         None
  37
  38         Returns
  39         -------
  40         string
  41         The error message
  42         """
  43         return self._msg
  44
  45 class Writer(object):
  46     """ Writer -- Provide common function for exporting signals into files
  47 The purpose of this class is to provide some basic functions to write the
  48 Signals to files (file validation) thus simplifying the definition of
  49 Writers for many different file formats.
  50
  51 The derived classes must redefine _get_format_name, _format_check and
  52 write_signals.
  53     """
  54     def __init__(self):
  55         """ Instanciate the Reader
  56
  57         Parameter
  58         ---------
  59         None
  60
  61         Returns
  62         -------
  63         Writer
  64         The object instanciated
  65         """
  66         self._fn = ""
  67         self._ow = False   # Overwrite flag
  68         self._opts = {}    # Options passed to write()
  69
  70     def write(self, fn, sigs, opts = {}):
  71         """ Do some checks before calling write_signals
  72
  73         Parameters
  74         ----------
  75         fn: string
  76         Path to the output file
  77
  78         sigs: dict of Signals
  79         List of Signals to write in the file
  80
  81         opts: dict of various data with strings as keys
  82         Options to be considered for the writing
  83
  84         Returns
  85         -------
  86         bool
  87         True if operation completed successfully
  88
  89         Raises
  90         ------
  91         WriteError
  92         In case of invalid path or invalid file format
  93         """
  94         if isinstance(opts, dict):
  95             self._opts = opts
  96         # Overwrite option
  97         if self._opts.has_key("ow"):
  98             if self._opts["ow"] in ['True', 'true', '1']:
  99                 self._ow = True
 100             else:
 101                 self._ow = False
 102         if self._check(fn) and self._format_check(sigs):
 103             return self.write_signals(sigs)
 104         else:
 105             return False
 106
 107     def _check(self, fn):
 108         """ Common checks on file access
 109
 110         Parameter
 111         ---------
 112         fn: string
 113         Path to the file to validate
 114
 115         Returns
 116         -------
 117         Nothing
 118
 119         Raises
 120         ------
 121         WriteError
 122         In case no file is specified, file exist and overwrite is not allowed
 123         or file access issue
 124         """
 125         if not (isinstance(fn, str) or isinstance(fn, unicode)):
 126             raise WriteError("No string specified")
 127         if not fn:
 128             raise WriteError("No file specified")
 129         if os.path.exists(fn):
 130             if not self._ow:
 131                 self._fn = fn
 132                 raise WriteError("File already exist")
 133             elif not os.path.isfile(fn):
 134                 raise WriteError("File exists but is not a file")
 135             elif not os.access(fn, os.W_OK):
 136                 raise WriteError("Cannot access file")
 137         elif not os.access(os.path.dirname(fn), os.W_OK):
 138             raise WriteError("Cannot access destination directory")
 139         self._fn = fn
 140         return True
 141
 142     def _format_check(self, sigs):
 143         """ Format specific checks, to be overridden by derived classes
 144
 145         Parameter
 146         ---------
 147         sigs: dict of Signals
 148         The Signal list to write
 149
 150         Returns
 151         -------
 152         bool
 153         True if no issue found to write the Signal list in this format
 154         """
 155         return False
 156
 157     def _get_format_name(self):
 158         """ Return the format name
 159
 160         Parameter
 161         ---------
 162         None
 163
 164         Returns
 165         -------
 166         string
 167         The format identifier
 168         """
 169         return None
 170
 171     def detect(self, format):
 172         """ Return True if format format is supported
 173
 174         Parameter
 175         ---------
 176         format: string
 177         Identifier of the whised format
 178
 179         Returns
 180         -------
 181         bool
 182         True if this Writer manage this format
 183         """
 184         if (isinstance(format, str) or isinstance(format, unicode))\
 185                 and format == self._get_format_name():
 186             return True
 187         else:
 188             return False
 189
 190     def write_signals(self, sigs):
 191         """ Write Signals to file
 192         This function must be redefined in the derived class
 193
 194         Parameter
 195         ---------
 196         sigs: dict of Signals
 197         The list of Signals to write
 198
 199         Returns
 200         -------
 201         Nothing
 202         """
 203         return