Question

我需要读取data.csv中的所有行，如果City列的值是Los Angeles，那么它将把该行添加到match.csv中，但是我不希望它创建带有标题的match.csv如果data.csv中“城市”列中没有洛杉矶的行，则为空行。我该怎么做？

with open("data.csv", 'r') as input_file, open("match.csv", 'w') as output_file:
    data_reader = csv.DictReader(input_file)
    match_write = csv.DictWriter(output_file, delimiter=',', fieldnames=data_reader.fieldnames)
    match_write.writeheader()
    for row in data_reader:
        if row['City'] == "Los Angeles":
            match_write.writerow(row)

Answer 1

如果您只是不想创建标题，并且可以使用空文件，那么请在洛杉矶的第一个实例之前不要创建作家。例如，除非在洛杉矶一行，否则不会将标头添加到文件match.csv：

match_write = None

with open("data.csv", 'r') as input_file, open("match.csv", 'w') as output_file:
    data_reader = csv.DictReader(input_file)
    for row in data_reader:
        if row['City'] == "Los Angeles":
            if match_write is None:
                match_write = csv.DictWriter(output_file, delimiter=',', fieldnames=data_reader.fieldnames)
                match_write.writeheader()
            match_write.writerow(row)

但是，如果除非有Los Angeles实例，否则根本不应该创建match.csv文件，那么在第一个实例之前都不应该打开文件。

output_file = None

with open("data.csv", 'r') as input_file:
    data_reader = csv.DictReader(input_file)
    for row in data_reader:
        if row['City'] == "Los Angeles":
            if output_file is None:
                output_file = open("match.csv", 'w')
                match_write = csv.DictWriter(output_file, delimiter=',', fieldnames=data_reader.fieldnames)
                match_write.writeheader()
            match_write.writerow(row)

if output_file is not None:
    output_file.close()

如何在Python中写入空文件之前检查条件？

1 个答案: