def impute_with_median (df):

    """Iterate through columns of Pandas DataFrame.

    Where NaNs exist replace with median"""

    # Get list of DataFrame column names

    cols = list(df)

    # Loop through columns

    for column in cols:

        # Transfer column to independent series

        col_data = df[column]

        # Look to see if there is any missing numerical data

        missing_data = sum(col_data.isna())

        if missing_data > 0:

            # Get median and replace missing numerical data with median

            col_median = col_data.median()

            col_data.fillna(col_median, inplace=True)

            df[column] = col_data

    return df

def plot_roc_curve(fpr, tpr, label=None):

    """Plot the ROC curve from False Positive Rate 

    and True Positive Rate"""

    plt.plot(fpr, tpr, linewidth=2, label=label)

    plt.plot([0, 1], [0, 1], 'k--') 

    plt.axis([0, 1, 0, 1])                       

    plt.xlabel('False Positive Rate', fontsize=16)

    plt.ylabel('True Positive Rate', fontsize=16)

    plt.grid(True)