使用fileinput和inplace=True修改文件内容：
import fileinput
import sys
for line in fileinput.input("test.txt",inplace=True):
# replaces all occurrences of apples in each line with oranges
sys.stdout.write(line.replace("apples","oranges"))
输入：
Marry has 10 carrots
Bob has 15 apples
Tom has 4 bananas
输出：
Marry has 10 carrots
Bob has 15 oranges
Tom has 4 bananas
使用re避免匹配子字符串：
import fileinput
import sys
import re
# use word boundaries so we only match "apples"
r = re.compile(r"\bapples\b")
for line in fileinput.input("test.txt",inplace=True):
# will write the line as is or replace apples with oranges and write
sys.stdout.write(r.sub("oranges",line))
删除所有遗留词：
import fileinput
import sys
for line in fileinput.input("test.txt",inplace=True):
# split on the last whitespace and write everything up to that
sys.stdout.write("{}\n".format(line.rsplit(None, 1)[0]))
输出：
Marry has 10
Bob has 15
Tom has 4
您还可以使用tempfile.NamedTemporaryFile使用以上任何逻辑将更新后的行写入，然后使用shutil.move替换原始文件：
from tempfile import NamedTemporaryFile
from shutil import move
with open("test.txt") as f, NamedTemporaryFile("w",dir=".", delete=False) as temp:
for line in f:
temp.write("{}\n".format(line.rsplit(None, 1)[0]))
# replace original file with updated content
move(temp.name,"test.txt")
您需要通过dir="."，delete=False因此当我们退出with时，文件文件不会被删除，我们可以使用.name属性访问该文件以传递给shutil。
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