⾯试题-python如何读取⼀个⼤于10G的txt⽂件？前⾔
⽤python 读取⼀个⼤于10G 的⽂件，⾃⼰电脑只有8G内存，⼀运⾏就报内存溢出：MemoryError
python 如何⽤open函数读取⼤⽂件呢？
读取⼤⽂件
⾸先可以⾃⼰先制作⼀个⼤于10G的txt⽂件
a = '''
2021-02-02 21:33:31,678 [quest:93] [base:get_response] [WARNING]- Not Found: /http:/123.125.114.144/
2021-02-02 21:33:31,679 [django.server:124] [basehttp:log_message] [WARNING]- "HEAD 123.125.114.144/ HTTP/1.1" 404 1678
2021-02-02 22:14:04,121 [django.server:124] [basehttp:log_message] [INFO]- code 400, message Bad request version ('HTTP')
2021-02-02 22:14:04,122 [django.server:124] [basehttp:log_message] [WARNING]- "GET ../../mnt/custom/ProductDefinition HTTP" 400 -
2021-02-02 22:16:21,052 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/login HTTP/1.1" 301 0
2021-02-02 22:16:21,123 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/login/ HTTP/1.1" 200 3876
2021-02-02 22:16:21,192 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/img/main_bg.png HTTP/1.1" 200 2801
2021-02-02 22:16:21,196 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/iconfont/style.css HTTP/1.1" 200 1638
2021-02-02 22:16:21,229 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/img/bg.jpg HTTP/1.1" 200 135990
2021-02-02 22:16:21,307 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/iconfont/f?u4m6fy HTTP/1.1" 200 6900
2021-02-02 22:16:23,525 [django.server:124] [basehttp:log_message] [INFO]- "POST /api/login/ HTTP/1.1" 302 0
2021-02-02 22:16:23,618 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/index/ HTTP/1.1" 200 18447
2021-02-02 22:16:23,709 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/js/commons.js HTTP/1.1" 200 13209
2021-02-02 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/css/admin.css HTTP/1.1" 200 19660
2021-02-02 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/css/common.css HTTP/1.1" 200 1004
2021-02-02 22:16:23,714 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/js/app.js HTTP/1.1" 200 20844
2021-02-02 22:16:26,509 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/report_list/1/ HTTP/1.1" 200 14649
2021-02-02 22:16:51,496 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/test_list/1/ HTTP/1.1" 200 24874
2021-02-02 22:16:51,721 [django.server:124] [basehttp:log_message] [INFO]- "POST /api/add_case/ HTTP/1.1" 200 0
2021-02-02 22:16:59,707 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/test_list/1/ HTTP/1.1" 200 24874
2021-02-03 22:16:59,909 [django.server:124] [basehttp:log_message] [INFO]- "POST /api/add_case/ HTTP/1.1" 200 0
2021-02-03 22:17:01,306 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/edit_case/1/ HTTP/1.1" 200 36504
2021-02-03 22:17:06,265 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/add_project/ HTTP/1.1" 200 17737
2021-02-03 22:17:07,825 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/project_list/1/ HTTP/1.1" 200 29789
2021-02-03 22:17:13,116 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/add_config/ HTTP/1.1" 200 24816
2021-02-03 22:17:19,671 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/config_list/1/ HTTP/1.1" 200 19532
'''
while True:
with open("xxx.log", "a", encoding="utf-8") as fp:
fp.write(a)
循环写⼊到 xxx.log ⽂件，运⾏ 3-5 分钟，pycharm 打开查看⽂件⼤⼩⼤于 10G
于是我⽤open函数直接读取
# 作者-上海悠悠 QQ交流:717225969
# blog地址 wwwblogs/yoyoketang/
f = open("xxx.log", 'r')
ad())
f.close()
抛出内存溢出异常:MemoryError
Traceback (most recent call last):
File "D:/2021kecheng06/demo/txt.py", line 35, in <module>
ad())
MemoryError
运⾏的时候可以看下⾃⼰电脑的内存已经占了100%， cpu⾼达91% ，不挂掉才怪了！
这种错误的原因在于，read()⽅法执⾏操作是⼀次性的都读⼊内存中，显然⽂件⼤于内存就会报错。
read() 的⼏种⽅法
f = open("xxx.log", 'r')
ad(2048))
f.close()
运⾏结果
2019-10-24 21:33:31,678 [quest:93] [base:get_response] [WARNING]- Not Found: /http:/123.125.114.144/
2019-10-24 21:33:31,679 [django.server:124] [basehttp:log_message] [WARNING]- "HEAD 123.125.114.144/ HTTP/1.1" 404 1678
2019-10-24 22:14:04,121 [django.server:124] [basehttp:log_message] [INFO]- code 400, message Bad request version ('HTTP')
2019-10-24 22:14:04,122 [django.server:124] [basehttp:log_message] [WARNING]- "GET ../../mnt/custom/ProductDefinition HTTP" 400 -
2019-10-24 22:16:21,052 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/login HTTP/1.1" 301 0
2019-10-24 22:16:21,123 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/login/ HTTP/1.1" 200 3876
2019-10-24 22:16:21,192 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/img/main_bg.png HTTP/1.1" 200 2801
2019-10-24 22:16:21,196 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/iconfont/style.css HTTP/1.1" 200 1638
2019-10-24 22:16:21,229 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/img/bg.jpg HTTP/1.1" 200 135990
2019-10-24 22:16:21,307 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/iconfont/f?u4m6fy HTTP/1.1" 200 6900
2019-10-24 22:16:23,525 [django.server:124] [basehttp:log_message] [INFO]- "POST /api/login/ HTTP/1.1" 302 0
2019-10-24 22:16:23,618 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/index/ HTTP/1.1" 200 18447
2019-10-24 22:16:23,709 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/js/commons.js HTTP/1.1" 200 13209
2019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/css/admin.css HTTP/1.1" 200 19660
2019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/css/common.css HTTP/1.1" 200 1004
2019-10-24 22:16:23,714 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/js/app.js HTTP/1.1" 200 20844
2019-10-24 22:16:26,509 [django.server:124] [basehttp:log_message] [I
这样就只读取了2048个字符，全部读取的话，循环读就⾏
# 作者-上海悠悠 QQ交流:717225969
# blog地址 wwwblogs/yoyoketang/
f = open("xxx.log", 'r')
while True:
block = f.read(2048)
print(block)
if not block:
break
f.close()
f = open("xxx.log", 'r')
while True:
line = f.readline()
print(line, end="")
if not line:
break
f.close()
真正 Pythonic 的⽅法
真正 Pythonci 的⽅法，使⽤ with 结构打开⽂件，fp 是⼀个可迭代对象，可以⽤ for 遍历读取每⾏的⽂件内容
with open("xxx.log", 'r') as fp:
for line in fp:
print(line, end="")
yield ⽣成器读取⼤⽂件
前⾯⼀篇讲yield ⽣成器的时候提到读取⼤⽂件，函数返回⼀个可迭代对象，⽤next()⽅法读取⽂件内容
# 作者-上海悠悠 QQ交流:717225969
# blog地址 wwwblogs/yoyoketang/
def read_file(fpath):
BLOCK_SIZE = 1024
with open(fpath, 'rb') as f:
while True:
block = f.read(BLOCK_SIZE)
if block:
yield block
else:
return
if __name__ == '__main__':
a = read_file("xxx.log")
print(a)            # generator objec
print(next(a))      # bytes类型
print(next(a).decode("utf-8"))  # str
运⾏结果
python怎么读文件夹下的文件夹<generator object read_file at 0x00000226B3005258>
b'\r\n2019-10-24 21:33:31,678 [quest:93] [base:get_response] [WARNING]- Not Found: /http:/123.125.114.144/\r\n2019-10-24 21:33:31,679 [django.server:124] [basehttp:log_message] [WARNING]- "HEAD 123.125.114.144/ HTTP/ [basehttp:log_message] [INFO]- "GET /static/assets/img/bg.jpg HTTP/1.1" 200 135990
2019-10-24 22:16:21,307 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/iconfont/f?u4m6fy HTTP/1.1" 200 6900
2019-10-24 22:16:23,525 [django.server:124] [basehttp:log_message] [INFO]- "POST /api/login/ HTTP/1.1" 302 0
2019-10-24 22:16:23,618 [django.server:124] [basehttp:log_message] [INFO]- "GET /api/index/ HTTP/1.1" 200 18447
2019-10-24 22:16:23,709 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/js/commons.js HTTP/1.1" 200 13209
2019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/css/admin.css HTTP/1.1" 200 19660
2019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/css/common.css HTTP/1.1" 200 1004
2019-10-24 22:16:23,714 [django.server:124] [basehttp:log_message] [INFO]- "GET /static/assets/js/app.js HTTP/1.1" 200 20844
2019-10-24 22:16:26,509 [django.server:124] [basehtt

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