chore: 添加虚拟环境到仓库

- 添加 backend_service/venv 虚拟环境
- 包含所有Python依赖包
- 注意：虚拟环境约393MB，包含12655个文件

backend_service/venv/lib/python3.13/site-packages/sympy/printing/python.py

@@ -0,0 +1,92 @@
+import keyword as kw
+import sympy
+from .repr import ReprPrinter
+from .str import StrPrinter
+
+# A list of classes that should be printed using StrPrinter
+STRPRINT = ("Add", "Infinity", "Integer", "Mul", "NegativeInfinity", "Pow")
+
+
+class PythonPrinter(ReprPrinter, StrPrinter):
+    """A printer which converts an expression into its Python interpretation."""
+
+    def __init__(self, settings=None):
+        super().__init__(settings)
+        self.symbols = []
+        self.functions = []
+
+        # Create print methods for classes that should use StrPrinter instead
+        # of ReprPrinter.
+        for name in STRPRINT:
+            f_name = "_print_%s" % name
+            f = getattr(StrPrinter, f_name)
+            setattr(PythonPrinter, f_name, f)
+
+    def _print_Function(self, expr):
+        func = expr.func.__name__
+        if not hasattr(sympy, func) and func not in self.functions:
+            self.functions.append(func)
+        return StrPrinter._print_Function(self, expr)
+
+    # procedure (!) for defining symbols which have be defined in print_python()
+    def _print_Symbol(self, expr):
+        symbol = self._str(expr)
+        if symbol not in self.symbols:
+            self.symbols.append(symbol)
+        return StrPrinter._print_Symbol(self, expr)
+
+    def _print_module(self, expr):
+        raise ValueError('Modules in the expression are unacceptable')
+
+
+def python(expr, **settings):
+    """Return Python interpretation of passed expression
+    (can be passed to the exec() function without any modifications)"""
+
+    printer = PythonPrinter(settings)
+    exprp = printer.doprint(expr)
+
+    result = ''
+    # Returning found symbols and functions
+    renamings = {}
+    for symbolname in printer.symbols:
+        # Remove curly braces from subscripted variables
+        if '{' in symbolname:
+            newsymbolname = symbolname.replace('{', '').replace('}', '')
+            renamings[sympy.Symbol(symbolname)] = newsymbolname
+        else:
+            newsymbolname = symbolname
+
+        # Escape symbol names that are reserved Python keywords
+        if kw.iskeyword(newsymbolname):
+            while True:
+                newsymbolname += "_"
+                if (newsymbolname not in printer.symbols and
+                        newsymbolname not in printer.functions):
+                    renamings[sympy.Symbol(
+                        symbolname)] = sympy.Symbol(newsymbolname)
+                    break
+        result += newsymbolname + ' = Symbol(\'' + symbolname + '\')\n'
+
+    for functionname in printer.functions:
+        newfunctionname = functionname
+        # Escape function names that are reserved Python keywords
+        if kw.iskeyword(newfunctionname):
+            while True:
+                newfunctionname += "_"
+                if (newfunctionname not in printer.symbols and
+                        newfunctionname not in printer.functions):
+                    renamings[sympy.Function(
+                        functionname)] = sympy.Function(newfunctionname)
+                    break
+        result += newfunctionname + ' = Function(\'' + functionname + '\')\n'
+
+    if renamings:
+        exprp = expr.subs(renamings)
+    result += 'e = ' + printer._str(exprp)
+    return result
+
+
+def print_python(expr, **settings):
+    """Print output of python() function"""
+    print(python(expr, **settings))