pandas-sample.py

import codecs

import pandas as pd
import numpy as np

# Shift-JISを読み込み
with codecs.open("sample.csv","r", encoding="sjis",errors="ignore") as f:
    df = pd.read_csv(f)

# 列を日付型に変換
df["date"] = pd.to_datetime(df["date"])

# col1のデータがなければ、col2の値を代入
df["col3"] = np.where(df["col1"] is None, df["col2"], df["col1"])

# 日付を年月形式に変換
df["year_month"] = df["date"].dt.strftime("%Y%m")

# 集計
pivot = pd.pivot_table(df, value="uriage", index="kokyaku", column="date", aggfunc="sum")

# Shift-JISで書き込み
with codecs.open("a.csv", "w", encoding="sjis", errors="ignore") as f:
    pivot.to_csv(f)