Explicitly check CASTEP version and error out if too low

euphonic/readers/castep.py

@@ -1,4 +1,5 @@
 from collections import defaultdict
+from packaging.version import Version
 import re
 import struct
 from typing import (Any, BinaryIO, Dict, Iterator, List, NamedTuple,
@@ -451,6 +452,17 @@ def read_interpolation_data(
         float_type = '>f8'
         first_cell_read = True
         while (header := _read_entry(f).strip()) != b'END':
+            if header == b'BEGIN_PARAMETERS_DUMP':
+                castep_version: Version = Version(_read_entry(f).decode().strip())
+                if castep_version < Version("17.1"):
+                    raise ValueError('Old castep file detected: '
+                        'Euphonic only supports post-Castep 17.1 files. '
+                        'Please rerun the calculation with a newer version '
+                        'of Castep with the original .cell file and a '
+                        '.castep file with a single line with the '
+                        '"continuation: <old.castep_bin>" keyword and '
+                        'use the new output .castep_bin file in Euphonic.')
+
             if header == b'BEGIN_UNIT_CELL':
                 # CASTEP writes the cell twice: the first is the
                 # geometry optimised cell, the second is the original
@@ -470,17 +482,8 @@ def read_interpolation_data(
                                (n_cells_in_sc, 3*n_atoms, 3*n_atoms)),
                     axes=[0, 2, 1]))
 
-                cell_origins = _read_entry(f, int_type)
-                if isinstance(cell_origins, int):
-                    raise ValueError('Old castep file detected: '
-                        'Euphonic only supports post-Castep 17.1 files. '
-                        'Please rerun the calculation with a newer version '
-                        'of Castep with the original .cell file and a '
-                        '.castep file with a single line with the '
-                        '"continuation: <old.castep_bin>" keyword and '
-                        'use the new output .castep_bin file in Euphonic.')
-
-                cell_origins = np.reshape(cell_origins, (n_cells_in_sc, 3))
+                cell_origins = np.reshape(_read_entry(f, int_type),
+                                          (n_cells_in_sc, 3))
 
                 _ = _read_entry(f, int_type)  # FC row not used
             elif header == b'BORN_CHGS':

setup.py

@@ -138,6 +138,7 @@ def run_setup():
         packages=packages,
         include_package_data=True,
         install_requires=[
+            'packaging',
             'scipy>=1.10',  # requires numpy >= 1.19.5
             'seekpath>=1.1.0',
             'spglib>=1.9.4',