Python：添加值并写入输出

Question

我需要从列表中获取信息，并从名称中获取add a column year。我仍然不确定如何在记录中添加一个字段'year'。 我可以使用追加吗？ 关于输出文件，我只需要使用outputcsv.writerow(records) 不是吗？ 这是我卡住的部分代码：

filenames = ('babyQld2010.csv',     
    'babyQld2011.csv',
    'babyQld2012.csv', 
    'babyQld2012.csv',
    'babyQld2014.csv')

outFile = open('babyQldAll.csv','w') 
csvFile_out = csv.writer(outFile, delimiter=',')

for filename in filenames:
    name, ext = filename.split('.')
    year = name[-4:]     #extract year from  file names
    records = extract_names(filename)

    # Get (name, count, gender)  from  list "records", 
    # and add value of "year" and write into output file (using "for" loop )

输出文件如下：

2010,Lola,69,Girl

然后输入，我有 5 个文件 babyQld2010.csv, babyQld2011.csv, babyQld2012.csv, babyQld2012.csv, babyQld2014.csv，其中包含：

Mia,425,William,493

我必须按格式对其进行排序，我已经完成并保存在列表中'records'

Lola,69,Girl

现在我需要添加一个字段'year' on 'record'列表并导出csv file。

这是我的完整代码：

import csv

def extract_names(filename):
    ''' Extract babyname, count, gender from a csv file,
    and return the data in a list.
    '''

    inFile = open(filename, 'rU')
    csvFile = csv.reader(inFile, delimiter=',')

    # Initialization
    records = []
    rowNum = 0

    for row in  csvFile:

        if rowNum != 0:

            # +++++ You code here ++++
            # Read each row of csv file and save information  in list 'records'
            # as (name, count, gender) 
            records.append([row[0], row[1], "Female"])
            records.append([row[2], row[3], "Male"])
            print('Process each row...')      

        rowNum += 1

    inFile.close()
    return(records)



#### Start main program  #####

filenames = ('babyQld2010.csv',     
    'babyQld2011.csv',
    'babyQld2012.csv', 
    'babyQld2012.csv',
    'babyQld2014.csv')

with open('babyQldAll.csv','w') as outFile:

    csvFile_out = csv.writer(outFile, delimiter=',')

    for filename in filenames:
        name, ext = filename.split('.')
        year = name.split('.')[0][-4:]     #extract year from  file names
        records = extract_names(filename)
        for record in records:
            csvFile_out.write([year] + record)
    print("Write in csv file...")     

outFile.close()

Answer 1

要从 csv 文件中获取年份，您可以简单地将字符串拆分为 '.'，然后从拆分的第一部分获取最后四个字符。示例 -

>>> s = 'babyQld2010.csv'
>>> s.split('.')[0][-4:]
'2010'

然后只需简单地遍历您说是正确的记录列表，对于 in 中的每个列表，使用列表连接创建一个以年份开头的新列表并将其写入 csv 文件。

我还建议您使用 with 语句打开要写入的文件（甚至在您从其他 csv 文件读取的函数中）。示例 -

filenames = ('babyQld2010.csv',     
    'babyQld2011.csv',
    'babyQld2012.csv', 
    'babyQld2012.csv',
    'babyQld2014.csv')

with open('babyQldAll.csv','w') as outFile:

    csvFile_out = csv.writer(outFile, delimiter=',')

    for filename in filenames:
        name, ext = filename.split('.')
        year = name.split('.')[0][-4:]     #extract year from  file names
        records = extract_names(filename)
        for record in records:
            csvFile_out.writerow([year] + record)

Answer 2

是的，您可以在从源文件中读取时将year 列附加到每一行。您可以将每一行作为字典读入和写出，以便在需要对其进行处理时使用现有的列标题来处理数据。

使用csv.DictWriter() 方法，您可以在设置时指定标题(fieldnames)。然后，您可以使用writeheader() 方法将它们写出来。

import csv
file_list = ['babyQld2010.csv',     
             'babyQld2011.csv',
             'babyQld2012.csv', 
             'babyQld2012.csv',
             'babyQld2014.csv']
outFile = open('babyQldAll.csv', 'wb')
csv_writer = csv.DictWriter(outFile, 
                            fieldnames=['name','count','gender','year'])
csv_write_out.writeheader()

for a_file in file_list:
    name,ext = a_file.split('.')
    year = name[-4:]
    with open(a_file, 'rb') as inFile:
        csv_read_in = csv.DictReader(inFile)
        for row in csv_read_in:
            row['year'] = year
            csv_writer.writerow(row)

outfile.close()

希望这会有所帮助。