Allow pre-Python 3.9 versions of importlib.resources

src/pyvalem/atom_data.py

@@ -38,6 +38,7 @@
 """
 
 import csv
+import platform
 
 try:
     import importlib.resources as pkg_resources
@@ -46,6 +47,8 @@
     # noinspection PyUnresolvedReferences
     import importlib_resources as pkg_resources
 
+PYTHON3_VERSION = int(platform.python_version_tuple()[1])
+
 
 class Atom:
     """Class representing an atom instance.
@@ -172,16 +175,12 @@ def float_or_none(f):
         return None
 
 
-# list of all the element symbols recognised by pyvalem:
-element_symbols = []
-# pre-built mapping between element symbols and Atom instances:
-atoms = {}
-# Atom data is from Meija et al., "Atomic weights of the elements 2013
-# (IUPAC Technical Report)", Pure Appl. Chem. 88(3), 265-291, 2016.
-# See https://ciaaw.org/atomic-weights.htm
-with pkg_resources.files("pyvalem").joinpath("_data_atomic_weights.txt").open(
-    "r", encoding="utf8"
-) as fi:
+def read_atom_data(fi, atoms):
+    """
+    Read atom data from open file handle fi into dictionary atoms, keyed by
+    element symbol.
+    """
+
     reader = csv.reader(fi, delimiter=",")
     header = ["Symbol", "Name", "Z", "atomic_weight", "atomic_weight_unc"]
     for row in reader:
@@ -193,17 +192,34 @@ def float_or_none(f):
         element_symbol = atom_args[0]
         element_symbols.append(element_symbol)
         atoms[element_symbol] = Atom(*atom_args)
+    return atoms
+
+
+# list of all the element symbols recognised by pyvalem:
+element_symbols = []
+# pre-built mapping between element symbols and Atom instances:
+atoms = {}
+# Atom data is from Meija et al., "Atomic weights of the elements 2013
+# (IUPAC Technical Report)", Pure Appl. Chem. 88(3), 265-291, 2016.
+# See https://ciaaw.org/atomic-weights.htm
+if PYTHON3_VERSION < 9:
+    # NB Python 3.8 and below use open_text:
+    with pkg_resources.open_text("pyvalem", "_data_atomic_weights.txt") as fi:
+        read_atom_data(fi, atoms)
+else:
+    # NB Python 3.9 and above use importlib.resources.files:
+    with pkg_resources.files("pyvalem").joinpath("_data_atomic_weights.txt").open(
+        "r", encoding="utf8"
+    ) as fi:
+        read_atom_data(fi, atoms)
+
+
+def read_isotope_data(fi, isotopes):
+    """
+    Read in isotope mass data from open file handle fi into dictionary isotopes,
+    keyed by isotope symbol (e.g. "46Ti").
+    """
 
-# pre-built mapping between element isotopic symbols and Isotope instances:
-isotopes = {}
-# Isotope data is from the AME2016 Atomic Mass Evaluation reports,
-# Huang et al., "The Ame2016 atomic mass evaluation (I)", Chinese Physics C41,
-# 030002 (2017); Wang et al., "The Ame2016 atomic mass evaluation (II)",
-# Chinese Physics C41, 030003 (2017).
-# See http://amdc.impcas.ac.cn/masstables/Ame2016/mass16.txt
-with pkg_resources.files("pyvalem").joinpath("_data_isotope_masses.txt").open(
-    "r", encoding="utf8"
-) as fi:
     reader = csv.reader(fi, delimiter=",")
     header = ["Z", "A", "Symbol", "mass", "mass_unc", "estimated_flag"]
     iso_attribs = [
@@ -229,3 +245,22 @@ def float_or_none(f):
         iso_symbol = "{:d}{:s}".format(iso_kwargs["mass_number"], iso_kwargs["symbol"])
         iso_kwargs["symbol"] = iso_symbol
         isotopes[iso_symbol] = Isotope(**iso_kwargs)
+
+
+# pre-built mapping between element isotopic symbols and Isotope instances:
+isotopes = {}
+# Isotope data is from the AME2016 Atomic Mass Evaluation reports,
+# Huang et al., "The Ame2016 atomic mass evaluation (I)", Chinese Physics C41,
+# 030002 (2017); Wang et al., "The Ame2016 atomic mass evaluation (II)",
+# Chinese Physics C41, 030003 (2017).
+# See http://amdc.impcas.ac.cn/masstables/Ame2016/mass16.txt
+if PYTHON3_VERSION < 9:
+    # NB Python 3.8 and below use open_text:
+    with pkg_resources.open_text("pyvalem", "_data_isotope_masses.txt") as fi:
+        read_isotope_data(fi, isotopes)
+else:
+    # NB Python 3.9 and above use importlib.resources.files:
+    with pkg_resources.files("pyvalem").joinpath("_data_isotope_masses.txt").open(
+        "r", encoding="utf8"
+    ) as fi:
+        read_isotope_data(fi, isotopes)