前言：学习处理文件，让程序快速分析大量数据；学习异常，管理程序运营时出现的错误；学习模块json, 保存用户数据。
10.1 文件读取
10.1.1 读取整个文件
with open('pi_digits.txt') as file_object:
#函数open() ;关键字with在不再需要访问文件后将其关闭；也可以调用open()和close()来打开和关闭；
contents = file_object.read()#read()读取内容，并保存为字符串，末尾会返回空字符串；可以用rstrip()删除
print(contents.rstrip())
10.1.2 文件路径
应用场景：要打开的文件不再程序文件所属目录中
- 使用相对文件路径
with open('text_files/filename.txt) as file_object: # linux和os系统; text_files 为文件夹名称
with open('text_files\filename.txt) as file_object: # windows 系统
- 使用绝对文件路径
file_path = '/home/ehmatthes/other_files/text_files/filename.txt' #linux 和os系统
with open(file_path) as file_object:
file_path = ' c:\home\ehmatthes\other_files\text_files\filename.txt' #win系统
with open(file_path) as file_object:
10.1.3 逐行读取
以每次一行的方式检查文件，可对文件对象使用for循环。
filename = 'pi_digits.txt'
with open(filename) as file_object:
for line in file_object:
print(line.rstrip())
10.1.4 创建包含文件各行内容的列表
filename = 'pi_digits.txt'
with open(filename) as file_object:
lines = file_object.readlines() #readlines()读取文件中的每一行，并将其存储在一个列表中
for line in lines: #存储后可在with代码块之外使用
print(line.rstrip())
10.1.5 使用文件内容
读取文本文件时，所有文本都解读为字符串。
如要作为数值，使用函数int()和float()
filename = 'pi_digits.txt'
with open(filename) as file_object:
lines = file_object.readlines()
pi_string = ''
for line in lines:
pi_string += line.strip()
print(pi_string)
print(len(pi_string))
10.1.6 包含一百万位的大型文件
filename = 'pi_million_digits.txt'
with open(filename) as file_object:
lines = file_object.readlines()
pi_string = ""
for line in lines:
pi_string += line.strip()
print(pi_string[:52]+ '...') #只打印小数点后50位
print(len(pi_string))
10.1.7 检查文件时否包含数据或字符串
filename = 'pi_million_digits.txt'
with open(filename) as file_object:
lines = file_object.readlines()
pi_string = ""
for line in lines:
pi_string += line.strip()
birthday = input('enter your birthday, in the form mmddyy:')
if birthday in pi_string:
print('your birthday appears in the first million digits of pi!')
else:
print('your birthday does not appear in the first million digits of pi.')
10.2 写入文件
10.2.1 写入空文件
Python只能写入字符串。如果存储数值，需先用函数str()将其转化为字符串格式。
filename = 'programming.txt'
with open(filename.'w') as file_object:m#读取模式r，写入模式w，附加模式a，读取和写入r+；若要写入的文件不存在则自动创建
file_object.write('i love programming.')# write()写入字符串
10.2.2 写入多行
函数write()不会在写入的文本末尾添加换行符，要让每个字符串都单独占一行，需要在write()语句中包含换行符。
filename = 'programming.txt'
with open(filename,'w') as file_object:
file_object.write('i love programming.\n')
file_object.write("i love creating new games.\n")#增加换行符，使写入的文本单独一行
10.2.3 附加到文件
给文件添加内容而不覆盖原有内容，用附加模式打开文件。
filename = 'programming.txt'
with open(filename,'a') as file_object:
file_object.write('i also love finding meaning in large datasets.\n')
file_object.write("i love creating apps that can run in a browser.\n")
10.3 异常
使用try-except代码块处理。
10.3.1 处理zerodivisionerror异常
try:
print(5/0)
except ZeroDivisionError:
print('you cannot divide by zero!')
10.3.2 使用异常避免崩溃
print("give me two numbers, and i'll divide them.")
print("enter 'q' to quit.")
while True:
first_number = input("\nfirst number: ")
if first_number == 'q':
break
second_number = input("\nsecond number: ")
if second_number == 'q':
break
try:
answer = int(first_number)/int(second_number)
except ZeroDivisionError:
print('you cannot divide by zero!')
else:
print(answer)
10.3.5 处理filenotfounderror异常
filename = 'alice.txt'
try:
with open(filename) as f:
contents = f.read()
except FileNotFoundError:
msg = "sorry,the file "+filename +'does not exist.'
print(msg)
10.3.6 分析文本
gutenberg 无版权限制的文学作品，可用来练习文本操作。
方法split()，以空格为分隔符，根据一个字符串创建一个单词列表.
filename = 'alice.txt'
try:
with open(filename) as f:
contents = f.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.')
10.3.7 使用多个文件
def count_words(filename):
"""计算一个文件大概包含多少单词"""
try:
with open(filename) as f:
contents = f.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)
10.3.8 pass 语句
def count_words(filename):
"""计算一个文件大概包含多少单词"""
try:
with open(filename) as f:
contents = f.read()
except FileNotFoundError:
pass # 出现异常时，直接执行except代码块中的语句
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)
10.4 存储数据
使用模块json（javascript object notation）存储数据
10.4.1 使用json.dump()和json.load()
import json #导入json模块
numbers = [2,3,5,7,11,13]
filename = 'number.json' #存储目标文件名称，数据为json格式
with open(filename,'w') as f: #写入模式打开这个文件，让json把数据写入
json.dump(numbers,f) #使用json.dump（）存储文件
import json
filename = 'numbers.json'
with open(filename) as f:
numbers = json.load(f) #加载数据
print(numbers)
10.4.2 保存和读取用户生成的数据
import json
#如果存储过用户名就加载它
#否则，提示用户输入用户名并存储它
filename = 'username.json'
try:
with open(filename) as f:
username = json.load(f)
except FileNotFoundError:
username = imput("what is your name?")
with open(filenme,'w') as f:
json.dump(username,f)
print("we'll remember you when you come back, " + username +"!")
else:
print("welcome back, " + username + "!")
10.4.3 重构
将代码划分为一系列完成具体工作的函数，让代码更清晰、更易于理解、更容易扩展
import json
def get_sorted_username():
"""如果存储了用户名就获取它"""
filename = "username.json"
try:
with open(filename) as f:
username = json.load(f)
except FileNotFoundError:
return None
else:
return username
def get_new_username():
"""提示输入用户名"""
username = input("what is your name?")
filename = "username.json"
with open(filename,'w') as f:
json.dump(username,f)
return username
def greet_user():
"""问候用户，并指出名字"""
username = get_sorted_username()
if username:
print("welcome back, " + username + "!")
else:
username = get_new_username()
print("we'll emember you when you come back, "+username +"!")
greet_user()
