爱站程序员基地前言
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 [django.request: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 http://123.125.114.144/ HTTP/1.1\" 404 16782021-02-02 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 02021-02-02 22:16:21,123 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/login/ HTTP/1.1\" 200 38762021-02-02 22:16:21,192 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/img/main_bg.png HTTP/1.1\" 200 28012021-02-02 22:16:21,196 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/iconfont/style.css HTTP/1.1\" 200 16ad8382021-02-02 22:16:21,229 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/img/bg.jpg HTTP/1.1\" 200 1359902021-02-02 22:16:21,307 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/iconfont/fonts/icomoon.ttf?u4m6fy HTTP/1.1\" 200 69002021-02-02 22:16:23,525 [django.server:124] [basehttp:log_message] [INFO]- \"POST /api/login/ HTTP/1.1\" 302 02021-02-02 22:16:23,618 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/index/ HTTP/1.1\" 200 184472021-02-02 22:16:23,709 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/js/commons.js HTTP/1.1\" 200 132092021-02-02 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/css/admin.css HTTP/1.1\" 200 196602021-02-02 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/css/common.css HTTP/1.1\" 200 10042021-02-02 22:16:23,714 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/js/app.js HTTP/1.1\" 200 208442021-02-02 22:16:26,509 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/report_list/1/ HTTP/1.1\" 200 146492021-02-02 22:16:51,496 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/test_list/1/ HTTP/1.1\" 200 248742021-02-02 22:16:51,721 [django.server:124] [basehttp:log_message] [INFO]- \"POST /api/add_case/ HTTP/1.1\" 200 02021-02-02 22:16:59,707 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/test_list/1/ HTTP/1.1\" 200 248742021-02-03 22:16:59,909 [django.server:124] [basehttp:log_message] [INFO]- \"POST /api/add_case/ HTTP/1.1\" 200 02021-02-03 22:17:01,306 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/edit_case/1/ HTTP/1.1\" 200 365042021-02-03 22:17:06,265 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/add_project/ HTTP/1.1\" 200 177372021-02-03 22:17:07,825 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/project_list/1/ HTTP/1.1\" 200 297892021-02-03 22:17:13,116 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/add_config/ HTTP/1.1\" 200 248162021-02-03 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
f = open(\"xxx.log\", \'r\')print(f.read())f.close()
抛出内存溢出异常:MemoryError
Traceback (most recent call last):File \"D:/2021kecheng06/demo/txt.py\", line56c35, in <module>print(f.read())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
1.read() 方法可以带参数 n， n 是每次读取的大小长度，也就是可以每次读一部分，这样就不会导致内存溢出
f = open(\"xxx.log\", \'r\')print(f.read(2048))f.close()
运行结果
2019-10-24 21:33:31,678 [django.request: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 http://123.125.114.144/ HTTP/1.1\" 404 16782019-10-24 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 02019-10-24 22:16:21,123 [dja56cngo.server:124] [basehttp:log_message] [INFO]- \"GET /api/login/ HTTP/1.1\" 200 38762019-10-24 22:16:21,192 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/img/main_bg.png HTTP/1.1\" 200 28012019-10-24 22:16:21,196 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/iconfont/style.css HTTP/1.1\" 200 16382019-10-24 22:16:21,229 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/img/bg.jpg HTTP/1.1\" 200 1359902019-10-24 22:16:21,307 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/iconfont/fonts/icomoon.ttf?u4m6fy HTTP/1.1\" 200 69002019-10-24 22:16:23,525 [django.server:124] [basehttp:log_message] [INFO]- \"POST /api/login/ HTTP/1.1\" 302 02019-10-24 22:16:23,618 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/index/ HTTP/1.1\" 200 184472019-10-24 22:16:23,709 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/js/commons.js HTTP/1.1\" 200 132092019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/css/admin.css HTTP/1.1\" 200 196602019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/css/common.css HTTP/1.1\" 200 10042019-10-24 22:16:23,714 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/js/app.js HTTP/1.1\" 200 208442019-10-24 22:16:26,509 [django.sead0rver: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
f = open(\"xxx.log\", \'r\')while True:block = f.read(2048)print(block)if not block:breakf.close()
2.readline()：每次读取一行，这个方法也不会报错
f = open(\"xxx.log\", \'r\')while True:line = f.readline()print(line, end=\"\")if not line:breakf.close()
3.readlines()：读取全部的行，生成一个list，通过list来对文件进行处理，显然这种方式依然会造成：MemoyError
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
def read_file(fpath):BLOCK_SIZE = 1024with open(fpath, \'rb\') as f:while True:block = f.read(BLOCK_SIZE)if block:yield blockelse:returnif __name__ == \'__main__\':a = read_file(\"xxx.log\")print(a) # generator objecprint(next(a)) # bytes类型print(next(a).decode(\"utf-8\")) # str
运行结果
<generator object read_file at 0x00000226B3005258>b\'\\r\\n2019-10-24 21:33:31,678 [django.request: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 http://123.125.114.144/ HTTP/1.1\" 404 1678\\r\\n2019-10-24 22:14:04,121 [django.server:124] [basehttp:log_message] [INFO]- code 400, message Bad request version (\\\'HTTP\\\')\\r\\n2019-10-24 22:14:04,122 [django.server:124] [basehttp:log_message] [WARNING]- \"GET ../../mnt/custom/ProductDefinition HTTP\" 400 -\\r\\n2019-10-24 22:16:21,052 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/login HTTP/1.1\" 301 0\\r\\n2019-10-24 22:16:21,123 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/login/ HTTP/1.1\" 200 3876\\r\\n2019-10-24 22:16:21,192 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/img/main_bg.png HTTP/1.1\" 200 2801\\r\\n2019-10-24 22:16:21,196 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/iconfont/style.css HTTP/1.1\" 200 1638\\r\\n2019-10-24 22:16:21,229 [django.server:124] \'[basehttp:log_messag1044e] [INFO]- \"GET /static/assets/img/bg.jpg HTTP/1.1\" 200 1359902019-10-24 22:16:21,307 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/iconfont/fonts/icomoon.ttf?u4m6fy HTTP/1.1\" 200 69002019-10-24 22:16:23,525 [django.server:124] [basehttp:log_message] [INFO]- \"POST /api/login/ HTTP/1.1\" 302 02019-10-24 22:16:23,618 [django.server:124] [basehttp:log_message] [INFO]- \"GET /api/index/ HTTP/1.1\" 200 184472019-10-24 22:16:23,709 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/js/commons.js HTTP/1.1\" 200 132092019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/css/admin.css HTTP/1.1\" 200 196602019-10-24 22:16:23,712 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/css/common.css HTTP/1.1\" 200 10042019-10-24 22:16:23,714 [django.server:124] [basehttp:log_message] [INFO]- \"GET /static/assets/js/app.js HTTP/1.1\" 200 208442019-10-24 22:16:26,509 [django.server:124] [basehtt
