crimes_by_month.py

def add_day_month_year(df):
    dates = df["Date"].map(lambda x: x[:10])
    df["day_of_month"] = dates.map(lambda x: x.split("/")[1])
    df["month"] = dates.map(lambda x: x.split("/")[0])
    df["year"] = dates.map(lambda x: x.split("/")[2])
    df["date"] = dates
    return df


from pandas import read_csv
crimes_df = read_csv("CrimeData.csv")
crimes_df = add_day_month_year(crimes_df)
crimes_df = crimes_df[crimes_df.year <= "2019"]

crimes_count_df = crimes_df \
    .groupby(["year", "month"]) \
    .size() \
    .to_frame("crimes") \
    .reset_index()

from calendar import monthrange
crimes_count_df["Days in month"] = crimes_count_df.apply(lambda row: monthrange(int(row.year), int(row.month))[1], axis=1)
crimes_count_df["Average crimes"] = crimes_count_df.apply(lambda row: row["crimes"] / row["Days in month"], axis=1)

df = crimes_count_df \
    .groupby(["month"])["Average crimes"] \
    .mean() \
    .reset_index()

print(crimes_count_df.to_string())