如何在python中將標題行復制到新的csv

Question

我似乎無法弄清楚如何將主行的標題行復制到匹配的行中……我需要在主csv中抓取第一行並將其寫入匹配行中，如果符合條件，則寫其余行。 ..

with open('master.csv', 'r') as master, open('match.csv', 'w') as matched:
    for line in master:
            if any(city in line.split('","')[5] for city in citys) and \
            any(state in line.split('","')[6] for state in states) and \
            not any(category in line.split('","')[2] for category in categorys):
                matched.write(line)

請幫忙。 我是python的新手，不知道如何使用熊貓或其他任何東西...

Answer 1

您可以只消耗文件的第一行來進行讀取，然后將其寫回到要寫入的文件中：

with open('master.csv', 'r') as master, open('match.csv', 'w') as matched:
    matched.write(next(master)) # can't use readline when iterating on the file afterwards

不過，看來其余部分確實需要csv模塊。 我將編輯答案以嘗試朝該方向嘗試

使用csv模塊，不需要那些不安全的split 。 逗號是默認的分隔符，引號也可以正確處理。 所以我只寫：

import csv
with open('master.csv', 'r') as master, open('match.csv', 'w') as matched:
    cr = csv.reader(master)
    cw = csv.writer(matched)
    cw.writerow(next(cr))  # copy title

    for row in cr:  # iterate on the rows, already organized as lists
        if any(city in row[5] for city in citys) and \
        any(state in row[6] for state in states) and \
        not any(category in row[2] for category in categorys):
            cw.writerow(row)

順便說一句，您的過濾器會檢查row[5]是否包含city ，但也許您想要完全匹配。 例如： "York"將匹配"New York" ，這可能不是您想要的。 所以我的建議是使用in檢查每個條件的字符串是否在字符串列表中：

import csv
with open('master.csv', 'r') as master, open('match.csv', 'w') as matched:
    cr = csv.reader(master)
    cw = csv.writer(matched)
    cw.writerow(next(cr))  # copy title
    for row in cr:
        if row[5] in citys and row[6] in states and not row[2] in categorys:
           cw.writerow(row)

使用生成器理解甚至可以一次寫入所有行，這甚至可以更好：

import csv
with open('master.csv', 'r') as master, open('match.csv', 'w') as matched:
    cr = csv.reader(master)
    cw = csv.writer(matched)
    cw.writerow(next(cr))  # copy title
    cw.writerows(row for row in cr if row[5] in citys and row[6] in states and not row[2] in categorys)

請注意， citys ， states和categorys最好使用set而不是list因此查找算法要快得多（您未提供該信息）

Answer 2

如果您不想過分考慮行產生迭代器的工作原理，那么一種簡單的方法是將第一行視為特殊：

with open('master.csv', 'r') as master, open('match.csv', 'w') as matched:
    first_line = True
    for line in master:
            if first_line or (any(city in line.split('","')[5] for city in citys) and \
            any(state in line.split('","')[6] for state in states) and \
            not any(category in line.split('","')[2] for category in categorys)):
                matched.write(line)
            first_line = False