Splitting out into multiple source files.

bitformat/__init__.py

@@ -27,13 +27,14 @@
 THE SOFTWARE.
 """
 
-__version__ = "0.0.1"
+__version__ = "0.0.2"
 
 __author__ = "Scott Griffiths"
 
 
 from bitstring import Bits, Dtype, Array
-from .format import Format, Field, Repeat, Find
+from .field import Field, Find
+from .format import Format, Repeat
 
 
 __all__ = ['Bits', 'Dtype', 'Format', 'Field', 'Array', 'Repeat', 'Find']

bitformat/common.py

@@ -0,0 +1,57 @@
+from __future__ import annotations
+import sys
+import ast
+
+indent_size = 4
+
+class Colour:
+    def __new__(cls, use_colour: bool) -> Colour:
+        x = super().__new__(cls)
+        if use_colour:
+            cls.blue = '\033[34m'
+            cls.purple = '\033[35m'
+            cls.green = '\033[32m'
+            cls.red = '\033[31m'
+            cls.cyan = '\033[36m'
+            cls.off = '\033[0m'
+        else:
+            cls.blue = cls.purple = cls.green = cls.red = cls.cyan = cls.off = ''
+        return x
+
+is_interactive_shell = hasattr(sys, 'ps1')
+colour = Colour(is_interactive_shell)
+
+
+class Expression:
+    def __init__(self, code_str: str):
+        code_str = code_str.strip()
+        if code_str[0] != '{' or code_str[-1] != '}':
+            raise ValueError(f"Invalid expression: '{code_str}'. It should start with '{{' and end with '}}'.")
+        self.code_str = code_str[1:-1].strip()
+        self.code = self.compile_safe_eval()
+        self.value = None
+
+    def compile_safe_eval(self):
+        # Only allowing operations for integer maths or boolean comparisons.
+        node_whitelist = {'BinOp', 'Name', 'Add', 'Expr', 'Mult', 'FloorDiv', 'Sub', 'Load', 'Module', 'Constant',
+                          'UnaryOp', 'USub', 'Mod', 'Pow', 'BitAnd', 'BitXor', 'BitOr', 'And', 'Or', 'BoolOp', 'LShift',
+                          'RShift', 'Eq', 'NotEq', 'Compare', 'LtE', 'GtE'}
+        nodes_used = set([x.__class__.__name__ for x in ast.walk(ast.parse(self.code_str))])
+        bad_nodes = nodes_used - node_whitelist
+        if bad_nodes:
+            raise ValueError(f"Disallowed operations used in expression '{self.code_str}'. Disallowed nodes were: {bad_nodes}.")
+        if '__' in self.code_str:
+            raise ValueError(f"Invalid expression: '{self.code_str}'. Double underscores are not permitted.")
+        code = compile(self.code_str, "<string>", "eval")
+        return code
+
+    def safe_eval(self, vars_: Dict[str, Any]) -> Any:
+        self.value = eval(self.code, {"__builtins__": {}}, vars_)
+        return self.value
+
+    def clear(self):
+        self.value = None
+
+    def __str__(self):
+        value_str = '' if self.value is None else f' = {self.value}'
+        return f'{{{self.code_str}{value_str}}}'