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import os
class Lockfile:
"""Prevent unwanted concurrency for file I/O.
For a file named "<file>", create or remove a lockfile named "<file>.lock".
When a process is modifying the file, call `lock(). When the modification
is done, call `unlock()`.
"""
def __init__(self, filepath):
self.filepath = filepath
self.lockpath = filepath + ".lock"
def lock(self):
"""Continue attempting to lock until locked."""
locked = False
while not locked:
try:
f = open(self.lockpath, "x")
f.close()
locked = True
except FileExistsError:
continue
def unlock(self):
"""Remove lockfile."""
try:
os.remove(self.lockpath)
except FileNotFoundError:
return
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