您的位置：首页 > 编程语言 > Python开发

Python学习笔记 Day11 文件和异常

2018-12-11 20:29 295 查看

Day 11 文件和异常

从文件读取数据一次性读取全部文件内容
```
with open('pi_digits.txt') as file_object:
contents =file_object.read()
```
函数open()用于打开文件，参数位文件名，返回值位文件对象；
关键字with在不需要访问文件后自动完成关闭工作；

逐行读取

file_name = "pi_digits.txt"
with open(file_name) as file_object:
for line in file_object:
print (line.rstrip())

从输出结果看，open返回的file_object应该是一个列表类型的变量；

关键字with结合open()返回的文件对象只在with代码块内可见，如需在with代码块外可见，则需创建一个列表对象，用于存储文件各行内容并留着在with代码块外使用；
```
with open(file_name) as file_object:
lines = file_object.readlines()
for line in lines:
print (line.rstrip())
```

使用文件内容

file_name = "pi_million_digits.txt"
with open(file_name) as file_object:
lines = file_object.readlines()
pi_string = ''
for line in lines:
pi_string += line.rstrip()
print (pi_string)
print (len(pi_string))

写入文件

with open(filename, ‘w’) as file_object:

filename = 'programming.txt'
with open(filename, 'w') as file_object:
file_object.write("I love programming!")

open的第二个实参： ‘r’：只读模式打开
’w’：写入模式打开
‘a’：附加模式打开
’r+‘：读取和写入模式打开
默认以只读方式打开文件。

异常

try expect else 代码块用于处理异常

try:
answer = int(first_number) / int(second_number)
except ZeroDivisionError:
print("You can't divide bu 0!")
else:
print(answer)

分析文本

filename = 'alice.txt'
try:
with open(filename) as f_obj:
contents = f_obj.read()
except FileNotFoundError:
msg = "Sorry, the file " + filename + " does not exist."
print(msg)
else:
#计算文件大致包含多少个单词
words = contents.split()
num_words = len(words)
print("The file " + filename + " has about " +
str(num_words) + " words.")

同时处理多个文件：将需要处理的文件名用列表存储

#定义计算文件有多少个单词的函数
def count_words(filename):
try:
with open(filename) as f_obj:
contents = f_obj.read()
except FileNotFoundError:
msg = "Sorry, the file " + filename + " does not exist."
print(msg)
else:
#计算文件大致包含多少个单词
words = contents.split()
num_words = len(words)
print("The file " + filename + " has about " +
str(num_words) + " words.")

filenames = ['alice.txt', 'siddhartha.txt', 'moby_dick.txt',
'little_women.txt']

for filename in filenames:
count_words(filename)

内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理

标签：

相关文章推荐

新的分享

章节导航