Adds tests for textual reel header with arbitrary content. Removes seek() calls from write_textual_reel_header() and write_binary_reel_header().

segpy/toolkit.py

@@ -576,7 +576,7 @@ def parse_template(template):
 
 
 def write_textual_reel_header(fh, lines, encoding):
-    """Write the SEG Y card image header, also known as the textual header
+    """Write the SEG Y card image header, also known as the textual header.
 
     Args:
         fh: A file-like object open in binary mode positioned such that the
@@ -594,7 +594,7 @@ def write_textual_reel_header(fh, lines, encoding):
             warning.  Any excess lines over CARDS_PER_HEADER will be discarded.  Short
             or omitted lines will be padded with spaces.
 
-        encoding: Typically 'cp037' for EBCDIC or 'ascii' for ASCII.
+        encoding: Either 'cp037' for EBCDIC or 'ascii' for ASCII.
 
     Post-condition:
         The file pointer in fh will be positioned at the first byte following the textual
@@ -607,16 +607,12 @@ def write_textual_reel_header(fh, lines, encoding):
     if not is_supported_encoding(encoding):
         raise UnsupportedEncodingError("Writing textual reel header", encoding)
 
-    fh.seek(0)
-
     padded_lines = [line.encode(encoding).ljust(CARD_LENGTH, ' '.encode(encoding))[:CARD_LENGTH]
                     for line in pad(lines, padding='', size=CARDS_PER_HEADER)]
     joined_header = EMPTY_BYTE_STRING.join(padded_lines)
     assert len(joined_header) == 3200
     fh.write(joined_header)
 
-    fh.seek(TEXTUAL_HEADER_NUM_BYTES)
-
 
 def write_binary_reel_header(fh, binary_reel_header, endian='>'):
     """Write the binary_reel_header to the given file-like object.
@@ -633,7 +629,6 @@ def write_binary_reel_header(fh, binary_reel_header, endian='>'):
     header_packer = make_header_packer(type(binary_reel_header), endian)
     buffer = header_packer.pack(binary_reel_header)
     fh.write(buffer)
-    fh.seek(REEL_HEADER_NUM_BYTES)
 
 
 def format_extended_textual_header(text, encoding, include_text_stop=False):

segpy/writer.py

@@ -14,7 +14,7 @@ def write_segy(fh,
                progress=None):
     """
     Args:
-        fh: A file-like object open for binary write.
+        fh: A file-like object open for binary write, positioned to write the textual reel header.
 
         seg_y_data:  An object from which the headers and trace_samples data can be retrieved. Requires the following
             properties and methods:

test/test_roundtrip.py

@@ -1,12 +1,15 @@
+from itertools import zip_longest
 import unittest
 from hypothesis import given
 from io import BytesIO
 from hypothesis.specifiers import sampled_from
 from segpy.binary_reel_header import BinaryReelHeader
+from segpy.encoding import ASCII, EBCDIC
 from segpy.header import are_equal
 
-from segpy.toolkit import write_binary_reel_header, read_binary_reel_header
-from test.strategies import header
+from segpy.toolkit import write_binary_reel_header, read_binary_reel_header, write_textual_reel_header, \
+    read_textual_reel_header, CARDS_PER_HEADER, CARD_LENGTH
+from test.strategies import header, multiline_ascii_encodable_text
 
 
 class TestBinaryReelHeader(unittest.TestCase):
@@ -16,9 +19,55 @@ class TestBinaryReelHeader(unittest.TestCase):
     def test_roundtrip(self, write_header, endian):
         with BytesIO() as write_stream:
             write_binary_reel_header(write_stream, write_header, endian)
-            written_steam = write_stream.getvalue()
+            written_stream = write_stream.getvalue()
 
-        with BytesIO(written_steam) as read_stream:
+        with BytesIO(written_stream) as read_stream:
             read_header = read_binary_reel_header(read_stream, endian)
 
         self.assertTrue(are_equal(write_header, read_header))
+
+
+class TestTextualReelHeader(unittest.TestCase):
+
+    @given(multiline_ascii_encodable_text(0, CARDS_PER_HEADER),
+           sampled_from([ASCII, EBCDIC]))
+    def test_roundtrip(self, write_header_text, encoding):
+        write_header_lines = write_header_text.splitlines()
+        with BytesIO() as write_stream:
+            write_textual_reel_header(write_stream, write_header_lines, encoding)
+            written_stream = write_stream.getvalue()
+
+        with BytesIO(written_stream) as read_stream:
+            read_header_lines = read_textual_reel_header(read_stream, encoding)
+
+        for written_line, read_line in zip_longest(write_header_lines[:CARDS_PER_HEADER],
+                                                   read_header_lines,
+                                                   fillvalue=""):
+            self.assertEqual(written_line[:CARD_LENGTH].rstrip().ljust(CARD_LENGTH),
+                             read_line)
+
+    @given(multiline_ascii_encodable_text(0, CARDS_PER_HEADER),
+           sampled_from([ASCII, EBCDIC]))
+    def test_header_num_lines(self, write_header_text, encoding):
+        write_header_lines = write_header_text.splitlines()
+        with BytesIO() as write_stream:
+            write_textual_reel_header(write_stream, write_header_lines, encoding)
+            written_stream = write_stream.getvalue()
+
+        with BytesIO(written_stream) as read_stream:
+            read_header_lines = read_textual_reel_header(read_stream, encoding)
+
+        self.assertEqual(len(read_header_lines), CARDS_PER_HEADER)
+
+    @given(multiline_ascii_encodable_text(0, CARDS_PER_HEADER),
+           sampled_from([ASCII, EBCDIC]))
+    def test_header_line_length(self, write_header_text, encoding):
+        write_header_lines = write_header_text.splitlines()
+        with BytesIO() as write_stream:
+            write_textual_reel_header(write_stream, write_header_lines, encoding)
+            written_stream = write_stream.getvalue()
+
+        with BytesIO(written_stream) as read_stream:
+            read_header_lines = read_textual_reel_header(read_stream, encoding)
+
+        self.assertTrue(all(len(line) == CARD_LENGTH for line in read_header_lines))