Parse header lines starting at the beginning of the line.

When reading a header file, each line is parsed by matching it against
a regular expression.  Previously, this was done by searching for the
pattern *anywhere* in the input line (using findall()) rather than at
the start of the line (using match()).

In particular, if the first token on the line (e.g., a signal file
name or segment name) contains a disallowed character, this must be
treated as an error, rather than silently ignoring everything up to
and including the disallowed character.

Note, however, that horizontal whitespace is permitted at the start of
the line, so the expressions must begin with "[ \t]*".

Author: Benjamin Moody

wfdb/io/_header.py

@@ -101,7 +101,8 @@
 # Regexp objects for reading headers
 # Record line
 _rx_record = re.compile(''.join(
-    ["(?P<record_name>[-\w]+)/?(?P<n_seg>\d*)[ \t]+",
+    ["[ \t]*",
+     "(?P<record_name>[-\w]+)/?(?P<n_seg>\d*)[ \t]+",
      "(?P<n_sig>\d+)[ \t]*(?P<fs>\d*\.?\d*)/*(?P<counter_freq>-?\d*\.?\d*)",
      "\(?(?P<base_counter>-?\d*\.?\d*)\)?[ \t]*(?P<sig_len>\d*)[ \t]*",
      "(?P<base_time>\d{,2}:?\d{,2}:?\d{,2}\.?\d{,6})[ \t]*",
@@ -110,7 +111,8 @@
 
 # Signal line
 _rx_signal = re.compile(''.join(
-    ["(?P<file_name>~?[-\w]*\.?[\w]*)[ \t]+(?P<fmt>\d+)x?"
+    ["[ \t]*",
+     "(?P<file_name>~?[-\w]*\.?[\w]*)[ \t]+(?P<fmt>\d+)x?"
      "(?P<samps_per_frame>\d*):?(?P<skew>\d*)\+?(?P<byte_offset>\d*)[ \t]*",
      "(?P<adc_gain>-?\d*\.?\d*e?[\+-]?\d*)\(?(?P<baseline>-?\d*)\)?",
      "/?(?P<units>[\w\^\-\?%\/]*)[ \t]*(?P<adc_res>\d*)[ \t]*",
@@ -119,7 +121,7 @@
 )
 
 # Segment line
-_rx_segment = re.compile('(?P<seg_name>[-\w]*~?)[ \t]+(?P<seg_len>\d+)')
+_rx_segment = re.compile('[ \t]*(?P<seg_name>[-\w]*~?)[ \t]+(?P<seg_len>\d+)')
 
 
 class BaseHeaderMixin(object):
@@ -879,11 +881,12 @@ def _parse_record_line(record_line):
     record_fields = {}
 
     # Read string fields from record line
+    match = _rx_record.match(record_line)
     (record_fields['record_name'], record_fields['n_seg'],
      record_fields['n_sig'], record_fields['fs'],
      record_fields['counter_freq'], record_fields['base_counter'],
      record_fields['sig_len'], record_fields['base_time'],
-     record_fields['base_date']) = re.findall(_rx_record, record_line)[0]
+     record_fields['base_date']) = match.groups()
 
     for field in RECORD_SPECS.index:
         # Replace empty strings with their read defaults (which are
@@ -942,14 +945,15 @@ def _parse_signal_lines(signal_lines):
 
     # Read string fields from signal line
     for ch in range(n_sig):
+        match = _rx_signal.match(signal_lines[ch])
         (signal_fields['file_name'][ch], signal_fields['fmt'][ch],
          signal_fields['samps_per_frame'][ch], signal_fields['skew'][ch],
          signal_fields['byte_offset'][ch], signal_fields['adc_gain'][ch],
          signal_fields['baseline'][ch], signal_fields['units'][ch],
          signal_fields['adc_res'][ch], signal_fields['adc_zero'][ch],
          signal_fields['init_value'][ch], signal_fields['checksum'][ch],
          signal_fields['block_size'][ch],
-         signal_fields['sig_name'][ch]) = _rx_signal.findall(signal_lines[ch])[0]
+         signal_fields['sig_name'][ch]) = match.groups()
 
         for field in SIGNAL_SPECS.index:
             # Replace empty strings with their read defaults (which are mostly None)
@@ -998,7 +1002,9 @@ def _read_segment_lines(segment_lines):
 
     # Read string fields from signal line
     for i in range(len(segment_lines)):
-        (segment_fields['seg_name'][i], segment_fields['seg_len'][i]) = _rx_segment.findall(segment_lines[i])[0]
+        match = _rx_segment.match(segment_lines[i])
+        (segment_fields['seg_name'][i],
+         segment_fields['seg_len'][i]) = match.groups()
 
         # Typecast strings for numerical field
         if field == 'seg_len':