Question

我有一个非常大的文件（3.8G），它是我学校系统中用户的摘录。我需要重新处理该文件，以便它只包含其ID和电子邮件地址，以逗号分隔。

我对此很少有经验，并希望将其用作Python的学习练习。

该文件的条目如下所示：

dn: uid=123456789012345,ou=Students,o=system.edu,o=system
LoginId: 0099886
mail: fflintstone@system.edu

dn: uid=543210987654321,ou=Students,o=system.edu,o=system
LoginId: 0083156
mail: brubble@system.edu

我正在尝试获取一个看起来像的文件：

0099886,fflintstone@system.edu
0083156,brubble@system.edu

任何提示或代码？

Answer 1

这对我来说实际上看起来像LDIF个文件。 python-ldap库有一个纯Python LDIF处理库，如果你的文件在LDIF中拥有一些令人讨厌的陷阱，它可以提供帮助，例如： Base64编码值，条目折叠等

您可以像这样使用它：

import csv
import ldif

class ParseRecords(ldif.LDIFParser):
   def __init__(self, csv_writer):
       self.csv_writer = csv_writer
   def handle(self, dn, entry):
       self.csv_writer.writerow([entry['LoginId'], entry['mail']])

with open('/path/to/large_file') as input, with open('output_file', 'wb') as output:
    csv_writer = csv.writer(output)
    csv_writer.writerow(['LoginId', 'Mail'])
    ParseRecords(input, csv_writer).parse()

修改

因此，要从实时LDAP目录中提取，使用python-ldap库，您可能希望执行以下操作：

import csv import ldap con = ldap.initialize('ldap://server.fqdn.system.edu') # if you're LDAP directory requires authentication # con.bind_s(username, password) try: with open('output_file', 'wb') as output: csv_writer = csv.writer(output) csv_writer.writerow(['LoginId', 'Mail']) for dn, attrs in con.search_s('ou=Students,o=system.edu,o=system', ldap.SCOPE_SUBTREE, attrlist = ['LoginId','mail']: csv_writer.writerow([attrs['LoginId'], attrs['mail']]) finally: # even if you don't have credentials, it's usually good to unbind con.unbind_s()

阅读documentation for the ldap module可能值得一读，尤其是example。

请注意，在上面的示例中，我完全跳过提供过滤器，您可能希望在生产中执行此过滤器。 LDAP中的过滤器类似于SQL语句中的WHERE子句;它限制返回的对象。 Microsoft actually has a good guide on LDAP filters。 LDAP过滤器的规范参考是RFC 4515。

同样，如果在应用适当的过滤器之后可能存在数千个条目，您可能需要查看LDAP paging control，尽管使用它会再次使示例更复杂。希望这足以让你开始，但如果有任何问题，请随时提出或打开一个新问题。
祝你好运。

Answer 2

假设每个条目的结构总是相同的，只需执行以下操作：

import csv

# Open the file
f = open("/path/to/large.file", "r")
# Create an output file
output_file = open("/desired/path/to/final/file", "w")

# Use the CSV module to make use of existing functionality.
final_file = csv.writer(output_file)

# Write the header row - can be skipped if headers not needed.
final_file.writerow(["LoginID","EmailAddress"])

# Set up our temporary cache for a user
current_user = []

# Iterate over the large file
# Note that we are avoiding loading the entire file into memory
for line in f:
    if line.startswith("LoginID"):
        current_user.append(line[9:].strip())
    # If more information is desired, simply add it to the conditions here
    # (additional elif's should do)
    # and add it to the current user.

    elif line.startswith("mail"):
        current_user.append(line[6:].strip())
        # Once you know you have reached the end of a user entry
        # write the row to the final file
        # and clear your temporary list.
        final_file.writerow(current_user)
        current_user = []

    # Skip lines that aren't interesting.
    else:
        continue

Answer 3

再次假设您的文件格式正确：

with open(inputfilename) as inputfile, with open(outputfilename) as outputfile:
    mail = loginid = ''
    for line in inputfile:
        line = inputfile.split(':')
        if line[0] not in ('LoginId', 'mail'):
            continue
        if line[0] == 'LoginId':
            loginid = line[1].strip()
        if line[0] == 'mail':
            mail = line[1].strip()
        if mail and loginid:
            output.write(loginid + ',' + mail + '\n')
            mail = loginid = ''

基本上等同于其他方法。

Answer 4

要打开文件，您需要使用类似with关键字的内容，以确保即使出现问题也能正常关闭：

with open(<your_file>, "r") as f:
   # Do stuff

至于实际解析该信息，我建议建立一个ID电子邮件对的字典。你还需要一个变量用于uid和电子邮件。

data = {}
uid = 0
email = ""

要实际解析文件（文件打开时运行的东西），您可以执行以下操作：

for line in f:
    if "uid=" in line:
        # Parse the user id out by grabbing the substring between the first = and ,
        uid = line[line.find("=")+1:line.find(",")]
    elif "mail:" in line:
        # Parse the email out by grabbing everything from the : to the end (removing the newline character)
        email = line[line.find(": ")+2:-1]
        # Given the formatting you've provided, this comes second so we can make an entry into the dict here
        data[uid] = email

使用CSV编写器（记得在文件开头导入csv）我们可以像这样输出：

writer = csv.writer(<filename>)
writer.writerow("User, Email")
for id, mail in data.iteritems:
    writer.writerow(id + "," + mail)

另一种选择是在文件之前打开编写器，写入标题，然后在写入CSV的同时从文件中读取行。这避免了将信息转储到内存中，这可能是非常需要的。所以把它们放在一起我们得到了

writer = csv.writer(<filename>)
writer.writerow("User, Email")
with open(<your_file>, "r") as f:
    for line in f:
        if "uid=" in line:
            # Parse the user id out by grabbing the substring between the first = and ,
            uid = line[line.find("=")+1:line.find(",")]
        elif "mail:" in line:
            # Parse the email out by grabbing everything from the : to the end (removing the newline character)
            email = line[line.find(": ")+2:-1]
            # Given the formatting you've provided, this comes second so we can make an entry into the dict here
            writer.writerow(iid + "," + email)

在python中处理大型文本文件

4 个答案: