add dnorm.py

src/pystats/dnorm.py

@@ -0,0 +1,45 @@
+# dnorm.py
+def dnorm(x, mean=0, sd=1, graph=True):
+    """
+    Calculates the Probability Density of the normal distribution at a given point and optionally plots the PDF.
+
+    Parameters
+    ----------
+    x : float
+        The point at which to evaluate the PDF.
+    mean : float, optional
+        The mean (average) of the normal distribution. Default is 0.
+    sd : float, optional
+        The standard deviation of the normal distribution. Default is 1.
+    graph : bool, optional
+        Whether to plot the PDF graph. Default is True.
+
+    Returns
+    -------
+    result_df : pandas.DataFrame
+        A DataFrame containing the input value and the corresponding PDF value.
+    result_graph : altair.Chart (optional)
+        An Altair Chart object visualizing the PDF with a marker at the specified x-value.
+        Returned only if `graph` is True.
+
+    Raises
+    ------
+    ValueError
+        If `sd` is zero or negative, as the standard deviation must be a positive number.
+    TypeError
+        If any of the input parameters (`x`, `mean`, `sd`) are not numerical.
+
+    Example
+    -------
+    >>> dnorm(1.96, mean=0, sd=1, graph=False)
+       x      PDF
+    0  1.96  0.058440
+
+    >>> result_df, result_graph = dnorm(1.96, mean=0, sd=1, graph=True)
+    >>> result_df
+       x      PDF
+    0  1.96  0.058440
+    >>> result_graph
+    # Displays the PDF plot with a marker at x=1.96
+    """
+    pass  # Function implementation will be added in a future milestone