Create a year-long histogram of counts of the variable for each month. It is
    assumed that the DataFrame index is datetime and that the variable
    `month_name` exists.

def histogram_month_counts(
    df,
    variable
    ):
    """
    Create a year-long histogram of counts of the variable for each month. It is
    assumed that the DataFrame index is datetime and that the variable
    `month_name` exists.
    """
    if not df.index.dtype in ["datetime64[ns]", "<M8[ns]", ">M8[ns]"]:
        log.error("index is not datetime")
        return False
    counts = df.groupby(df.index.strftime("%B"))[variable].count().reindex(calendar.month_name[1:])
    counts.plot(kind = "bar", width = 1, rot = 0, alpha = 0.7)