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/plotting/textplot.py

@@ -0,0 +1,168 @@
+from sympy.core.numbers import Float
+from sympy.core.symbol import Dummy
+from sympy.utilities.lambdify import lambdify
+
+import math
+
+
+def is_valid(x):
+    """Check if a floating point number is valid"""
+    if x is None:
+        return False
+    if isinstance(x, complex):
+        return False
+    return not math.isinf(x) and not math.isnan(x)
+
+
+def rescale(y, W, H, mi, ma):
+    """Rescale the given array `y` to fit into the integer values
+    between `0` and `H-1` for the values between ``mi`` and ``ma``.
+    """
+    y_new = []
+
+    norm = ma - mi
+    offset = (ma + mi) / 2
+
+    for x in range(W):
+        if is_valid(y[x]):
+            normalized = (y[x] - offset) / norm
+            if not is_valid(normalized):
+                y_new.append(None)
+            else:
+                rescaled = Float((normalized*H + H/2) * (H-1)/H).round()
+                rescaled = int(rescaled)
+                y_new.append(rescaled)
+        else:
+            y_new.append(None)
+    return y_new
+
+
+def linspace(start, stop, num):
+    return [start + (stop - start) * x / (num-1) for x in range(num)]
+
+
+def textplot_str(expr, a, b, W=55, H=21):
+    """Generator for the lines of the plot"""
+    free = expr.free_symbols
+    if len(free) > 1:
+        raise ValueError(
+            "The expression must have a single variable. (Got {})"
+            .format(free))
+    x = free.pop() if free else Dummy()
+    f = lambdify([x], expr)
+    if isinstance(a, complex):
+        if a.imag == 0:
+            a = a.real
+    if isinstance(b, complex):
+        if b.imag == 0:
+            b = b.real
+    a = float(a)
+    b = float(b)
+
+    # Calculate function values
+    x = linspace(a, b, W)
+    y = []
+    for val in x:
+        try:
+            y.append(f(val))
+        # Not sure what exceptions to catch here or why...
+        except (ValueError, TypeError, ZeroDivisionError):
+            y.append(None)
+
+    # Normalize height to screen space
+    y_valid = list(filter(is_valid, y))
+    if y_valid:
+        ma = max(y_valid)
+        mi = min(y_valid)
+        if ma == mi:
+            if ma:
+                mi, ma = sorted([0, 2*ma])
+            else:
+                mi, ma = -1, 1
+    else:
+        mi, ma = -1, 1
+    y_range = ma - mi
+    precision = math.floor(math.log10(y_range)) - 1
+    precision *= -1
+    mi = round(mi, precision)
+    ma = round(ma, precision)
+    y = rescale(y, W, H, mi, ma)
+
+    y_bins = linspace(mi, ma, H)
+
+    # Draw plot
+    margin = 7
+    for h in range(H - 1, -1, -1):
+        s = [' '] * W
+        for i in range(W):
+            if y[i] == h:
+                if (i == 0 or y[i - 1] == h - 1) and (i == W - 1 or y[i + 1] == h + 1):
+                    s[i] = '/'
+                elif (i == 0 or y[i - 1] == h + 1) and (i == W - 1 or y[i + 1] == h - 1):
+                    s[i] = '\\'
+                else:
+                    s[i] = '.'
+
+        if h == 0:
+            for i in range(W):
+                s[i] = '_'
+
+        # Print y values
+        if h in (0, H//2, H - 1):
+            prefix = ("%g" % y_bins[h]).rjust(margin)[:margin]
+        else:
+            prefix = " "*margin
+        s = "".join(s)
+        if h == H//2:
+            s = s.replace(" ", "-")
+        yield prefix + " |" + s
+
+    # Print x values
+    bottom = " " * (margin + 2)
+    bottom += ("%g" % x[0]).ljust(W//2)
+    if W % 2 == 1:
+        bottom += ("%g" % x[W//2]).ljust(W//2)
+    else:
+        bottom += ("%g" % x[W//2]).ljust(W//2-1)
+    bottom += "%g" % x[-1]
+    yield bottom
+
+
+def textplot(expr, a, b, W=55, H=21):
+    r"""
+    Print a crude ASCII art plot of the SymPy expression 'expr' (which
+    should contain a single symbol, e.g. x or something else) over the
+    interval [a, b].
+
+    Examples
+    ========
+
+    >>> from sympy import Symbol, sin
+    >>> from sympy.plotting import textplot
+    >>> t = Symbol('t')
+    >>> textplot(sin(t)*t, 0, 15)
+     14 |                                                  ...
+        |                                                     .
+        |                                                 .
+        |                                                      .
+        |                                                .
+        |                            ...
+        |                           /   .               .
+        |                          /
+        |                         /      .
+        |                        .        .            .
+    1.5 |----.......--------------------------------------------
+        |....       \           .          .
+        |            \         /                      .
+        |             ..      /             .
+        |               \    /                       .
+        |                ....
+        |                                    .
+        |                                     .     .
+        |
+        |                                      .   .
+    -11 |_______________________________________________________
+         0                          7.5                        15
+    """
+    for line in textplot_str(expr, a, b, W, H):
+        print(line)