python - python 2.6 linecache.getline() 和标准输入。它是如何工作的?
问题描述
我有一个脚本,它通过输入行来查找 ID 字符串的出现,同时跟踪行号。然后它向后运行输入以跟踪 parentID/childID 关系。该脚本接受使用“-f”标志作为参数的日志文件或来自管道的标准输入内容。作为输入部分的日志文件工作得很好,但从标准输入读取似乎不起作用。
为了合理清楚起见,我已经包含了与此相关的脚本部分,但不要期望能够运行它。这只是为了向您展示正在发生的事情(任何从事 FIX 协议金融服务工作的人都会认识到一些事情):
import os
import sys
import linecache
from types import *
from ____ import FixMessage # custom message class that is used throughout
# Feel free to ignore all the getArgs and validation crap
def getArgs():
import argparse
parser = argparse.ArgumentParser(
description='Get amendment history.')
parser.add_argument('-f', '--file',
help="input logfile.'")
args = parser.parse_args()
return validateArgs(args)
def validateArgs(args):
try:
if sys.stdin.isatty():
if args.file:
assert os.path.isfile(args.file.strip('\n')), \
'File "{0}" does not exist'.format(args.file)
args.file = open(args.file, 'r')
else:
args.file = sys.stdin
assert args.file, \
"Please either include a file with '-f' or pipe some text in"
except AssertionError as err:
print err
exit(1)
return args
defGetMessageTrail(logfile, orderId):
# some input validation
if isinstance(logfile, StringType):
try: logfile = open(logfile, 'r')
except IOError as err: exit(1)
elif not isinstance(logfile, FileType):
raise TypeError(
'Expected FileType and got {0}'.format(type(logfile)))
linenum = 0
# This retrieves the message containing the orderID as well as the linenum
for line in logfile:
linenum += 1
if orderId in line:
# FixMessage is a custom class that is treated here like
# a dictionary with some metadata
# Missing dict keys return 'None'
# .isvalid is bool results of some text validation
# .direction is either incoming or outgoing
# thats all you really need to know
msg = FixMessage(line)
if msg.isvalid and msg.direction == 'Incoming':
yield msg
break
# If there is a message parentID, it would be in msg['41']
if msg['41']:
messages = findParentMessages(logfile, startline=linenum, msg['41'])
for msg in messages: yield msg
def findParentMessages(logfile, startline, targetId):
# Some more input validation
assert isinstance(logfile, FileType)
assert isinstance(startline, IntType)
assert isinstance(targetId, StringType)
# should just make a integer decrementing generator,
# but this is fine for the example
for linenum in range(startline)[::-1]:
# *** This is where the question lies... ***
# print(logfile.name) # returns "<stdin>"
line = linecache.getline(logfile.name, linenum)
if 'Incoming' in line and '11=' + targetId in line:
msg = FixMessage(line)
yield msg
if msg['41']: findParentMessages(logfile, linenum, msg['41'])
else: break
def main():
log = getArgs().file
trail = getMessageTrail(log, 'ORDER123')
if __name__ == '__main__': main()
问题是,在将标准输入作为文件读取时,linecache.getline 是如何工作的?如果给定一个常规文件名,它与它的工作方式有什么不同吗?
解决方案
linecache.getline() 接受文件名,而不是文件对象。当文件名被传递给诸如 open() 和 os.stat() 之类的调用时,它的设计并不是这样工作的。
供参考:https ://github.com/python/cpython/blob/2.6/Lib/linecache.py
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