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1 #!/usr/bin/env python2.7
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2 # tsv.py: a module for writing TSV (tab-separated value) files
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3 """
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4 This module defines two classes: a TsvWriter, which can be constructed on a
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5 stream to allow writing TSV data lines and #-delimited comments to that stream,
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6 and a TsvReader, which can be constructed on a stream and iterated over to
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7 obtain lists of the values from each non-comment line in the stream.
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8
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9 TSV is most useful as the basis for other, more tightly specified file formats.
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10
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11 """
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12
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13 class TsvWriter(object):
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14 """
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15 Represents a writer for tab-separated value files containing #-delimited
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16 comments.
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17
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18 """
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19 def __init__(self, stream):
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20 """
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21 Make a new TsvWriter for writing TSV data to the given stream.
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22 """
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23
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24 # This holds the stream
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25 self.stream = stream
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26
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27
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28 def line(self, *args):
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29 """
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30 Write the given values to the file, as a TSV line. Args holds a list of
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31 all arguments passed. Any argument that stringifies to a string legal as
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32 a TSV data item can be written.
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33
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34 """
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35
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36 self.list_line(args)
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37
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38
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39 def list_line(self, line):
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40 """
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41 Write the given iterable of values (line) to the file as items on the
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42 same line. Any argument that stringifies to a string legal as a TSV data
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43 item can be written.
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44
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45 Does not copy the line or build a big string in memory.
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46 """
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47
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48 if len(line) == 0:
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49 return
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50
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51 self.stream.write(str(line[0]))
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52
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53 for item in line[1:]:
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54 self.stream.write("\t")
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55 self.stream.write(str(item))
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56
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57 self.stream.write("\n")
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58
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59 def comment(self, text):
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60 """
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61 Write the given text as a TSV comment. text must be a string containing
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62 no newlines.
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63
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64 """
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65
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66 self.stream.write("# {}\n".format(text))
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67
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68 def close(self):
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69 """
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70 Close the underlying stream.
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71 """
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72
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73 self.stream.close()
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74
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75 class TsvReader(object):
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76 """
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77 Represents a reader for tab-separated value files. Skips over comments
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78 starting with #. Can be iterated over.
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79
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80 Field values consisting of only whitespace are not allowed.
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81 """
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82
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83 def __init__(self, stream):
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84 """
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85 Make a new TsvReader to read from the given stream.
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86 """
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87
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88 self.stream = stream
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89
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90 def __iter__(self):
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91 """
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92 Yields lists of all fields on each line, as strings, until all lines are
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93 exhausted. Strips whitespace around field contents.
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94 """
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95
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96 for line in self.stream:
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97 line = line.strip()
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98 if line == "" or line[0] == "#":
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99 # Skip comments and empty lines
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100 continue
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101
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102 yield map(str.strip, line.split("\t"))
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103
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104 def close(self):
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105 """
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106 Close the underlying stream.
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107 """
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108
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109 self.stream.close()
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