tools/mpy-tool.py: Make global qstr list a dedicated class.

Signed-off-by: Damien George <damien@micropython.org>

tools/mpy-tool.py

@@ -91,19 +91,6 @@ class Config:
 config = Config()
 
 
-class QStrType:
-    def __init__(self, str):
-        self.str = str
-        self.qstr_esc = qstrutil.qstr_escape(self.str)
-        self.qstr_id = "MP_QSTR_" + self.qstr_esc
-
-
-# Initialise global list of qstrs with static qstrs
-global_qstrs = [None]  # MP_QSTRnull should never be referenced
-for n in qstrutil.static_qstr_list:
-    global_qstrs.append(QStrType(n))
-
-
 MP_CODE_BYTECODE = 2
 MP_CODE_NATIVE_PY = 3
 MP_CODE_NATIVE_VIPER = 4
@@ -469,6 +456,29 @@ def extract_prelude(bytecode, ip):
     )
 
 
+class QStrType:
+    def __init__(self, str):
+        self.str = str
+        self.qstr_esc = qstrutil.qstr_escape(self.str)
+        self.qstr_id = "MP_QSTR_" + self.qstr_esc
+
+
+class GlobalQStrList:
+    def __init__(self):
+        # Initialise global list of qstrs with static qstrs
+        self.qstrs = [None]  # MP_QSTRnull should never be referenced
+        for n in qstrutil.static_qstr_list:
+            self.qstrs.append(QStrType(n))
+
+    def add(self, s):
+        q = QStrType(s)
+        self.qstrs.append(q)
+        return q
+
+    def get_by_index(self, i):
+        return self.qstrs[i]
+
+
 class MPFunTable:
     def __repr__(self):
         return "mp_fun_table"
@@ -496,10 +506,6 @@ class CompiledModule:
         self.raw_code = raw_code
         self.escaped_name = escaped_name
 
-    def _unpack_qstr(self, ip):
-        qst = self.bytecode[ip] | self.bytecode[ip + 1] << 8
-        return global_qstrs[qst]
-
     def hexdump(self):
         with open(self.mpy_source_file, "rb") as f:
             WIDTH = 16
@@ -1077,8 +1083,7 @@ class RawCodeNative(RawCode):
             if qi < len(self.qstr_links) and i == self.qstr_links[qi][0]:
                 # link qstr
                 qi_off, qi_kind, qi_val = self.qstr_links[qi]
-                qst = global_qstrs[qi_val].qstr_id
-                i += self._link_qstr(i, qi_kind, qst)
+                i += self._link_qstr(i, qi_kind, qi_val.qstr_id)
                 qi += 1
             else:
                 # copy machine code (max 16 bytes)
@@ -1139,17 +1144,15 @@ def read_qstr(reader, segments):
     ln = reader.read_uint()
     if ln & 1:
         # static qstr
-        segments.append(
-            MPYSegment(MPYSegment.META, global_qstrs[ln >> 1].str, start_pos, start_pos)
-        )
-        return ln >> 1
+        q = global_qstrs.get_by_index(ln >> 1)
+        segments.append(MPYSegment(MPYSegment.META, q.str, start_pos, start_pos))
+        return q
     ln >>= 1
     start_pos = reader.tell()
     data = str_cons(reader.read_bytes(ln), "utf8")
     reader.read_byte()  # read and discard null terminator
     segments.append(MPYSegment(MPYSegment.QSTR, data, start_pos, reader.tell()))
-    global_qstrs.append(QStrType(data))
-    return len(global_qstrs) - 1
+    return global_qstrs.add(data)
 
 
 def read_obj(reader, segments):
@@ -1304,8 +1307,7 @@ def read_mpy(filename):
         # Read qstrs and construct qstr table.
         qstr_table = []
         for i in range(n_qstr):
-            q = read_qstr(reader, segments)
-            qstr_table.append(global_qstrs[q])
+            qstr_table.append(read_qstr(reader, segments))
 
         # Read objects and construct object table.
         obj_table = []
@@ -1345,7 +1347,7 @@ def disassemble_mpy(compiled_modules):
 def freeze_mpy(base_qstrs, compiled_modules):
     # add to qstrs
     new = {}
-    for q in global_qstrs:
+    for q in global_qstrs.qstrs:
         # don't add duplicates
         if q is None or q.qstr_esc in base_qstrs or q.qstr_esc in new:
             continue
@@ -1587,6 +1589,8 @@ def merge_mpy(raw_codes, output_file):
 
 
 def main():
+    global global_qstrs
+
     import argparse
 
     cmd_parser = argparse.ArgumentParser(description="A tool to work with MicroPython .mpy files.")
@@ -1637,6 +1641,9 @@ def main():
         config.MICROPY_QSTR_BYTES_IN_HASH = 1
         base_qstrs = list(qstrutil.static_qstr_list)
 
+    # Create initial list of global qstrs.
+    global_qstrs = GlobalQStrList()
+
     # Load all .mpy files.
     try:
         compiled_modules = [read_mpy(file) for file in args.files]