自学教程：python读取一个大于10G的txt文件的方法

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 16382021-02-02 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", line 35, 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 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/fonts/icomoon.ttf?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

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 = 1024    with open(fpath, 'rb') as f:        while True:            block = f.read(BLOCK_SIZE)            if block:                yield block            else:                returnif __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

<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_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/fonts/icomoon.ttf?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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