习题14

from sys import argv

script, user_name, age = argv
prompt = "Your answer: "

print(f"Hi {user_name}, I'm the {script} script.")
print("I'd like to ask you a few questions.")

print(f"Do you like me {user_name}?")
likes = input(prompt)

print(f"Where do you live {user_name}?")
lives = input(prompt)

print("What kind of computer do you have?")
computer = input(prompt)

print(f"""
Alright, so you said {likes} about liking me.
You live in {lives}.    Not sure where that is.
You are {age} years old now.
And you have a {computer} computer.     Nice.
""")
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PS D:\pythonp> python .\ex14.py h 24
Hi h, I'm the .\ex14.py script.
I'd like to ask you a few questions.
Do you like me h?
Your answer: y
Where do you live h?
Your answer: C
What kind of computer do you have?
Your answer: m

Alright, so you said y about liking me.
You live in C.    Not sure where that is.
You are 24 years old now.
And you have a m computer.     Nice.
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习题15 读取文件

代码

# 将sys模块导入
from sys import argv

# 将argv解包，将所有的参数依次赋值给左边的变量
script, filename = argv

# 打开filename文件，并将该文件赋值给txt
txt = open(filename)

# 打印格式化字符串，“这是你的文件xxx：”
print(f"Here's your file {filename}:")
# 读取并打印txt的全部内容
print(txt.read())

# 打印“再次输入文件名”
print("Type the filename again")
# 打印“>”符号，并将输入的内容赋值给file_again
file_again = input(">")

# 打开file_again文件，并将文件赋值给txt_again
txt_again = open(file_again)

# 读取并打印txt_again的全部内容
print(txt_again.read())

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ex15_sample.txt内容

This is stuff I typed into a file.
It is really a cool stuff.
Lots and lots fun to have in here.
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输出结果

PS D:\pythonp> python ex15.py ex15_sample.txt
Here's your file ex15_sample.txt:
This is stuff I typed into a file.
It is really a cool stuff.
Lots and lots fun to have in here.

Type the filename again
>ex15_sample.txt
This is stuff I typed into a file.
It is really a cool stuff.
Lots and lots fun to have in here.
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1. 删掉第10~15行用到 input的部分，再运行一遍脚本。

from sys import argv

script, filename = argv

txt = open(filename)

print(f"Here's your file {filename}:")
print(txt.read())
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PS D:\pythonp> python ex15.1.py ex15_sample.txt
Here's your file ex15_sample.txt:
This is stuff I typed into a file.
It is really a cool stuff.
Lots and lots fun to have in here.
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2. 只用 input写这个脚本，想想哪种获取文件名称的方法更好，为什么。

filename = input("Type the filename:")

txt = open(filename)

print(f"Here is your file {filename}:")
print(txt.read())
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PS D:\pythonp> python .\ex15.2.py
Type the filename:ex15_sample.txt
Here is your file ex15_sample.txt:
This is stuff I typed into a file.
It is really a cool stuff.
Lots and lots fun to have in here.
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3. 再次运行 python3.6，在提示符下使用open打开一个文件。注意这种在 python里边打开文件执行read的方式。

错误1：

PS D:\pythonp> python
Python 3.8.1 (tags/v3.8.1:1b293b6, Dec 18 2019, 23:11:46) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> txt=open(ex15_sample.txt)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'ex15_sample' is not defined
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• txt=open(ex15_sample.txt)
  文件名没有加路径

错误2

>>> txt=open(d:/pythonp/ex15_sample.txt)
  File "<stdin>", line 1
    txt=open(d:/pythonp/ex15_sample.txt)
              ^
SyntaxError: invalid syntax
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• open（）函数中路径及文件名没有加引号
  我也不知道为啥，反正加了就可以正常运行了，不是说变量名不加引号么？因为这是文件名？可是当其保存为py文件而不是在python运行下的时候，也没加引号就可以正常运行啊？

正确版本：

PS D:\pythonp> python
Python 3.8.1 (tags/v3.8.1:1b293b6, Dec 18 2019, 23:11:46) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> txt=open("d:/pythonp/ex15_sample.txt")
>>> txt.read()
'This is stuff I typed into a file.\nIt is really a cool stuff.\nLots and lots fun to have in here.\n'
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4. 让你的脚本针对txt和txt again变量也调用一下close（）。处理完文件后需要将其关闭，这是很重要的一点。

from sys import argv

script, filename = argv

txt = open(filename)

print(f"Here's your file {filename}:")
print(txt.read())

print("Type the filename again")
file_again = input(">")

txt_again = open(file_again)

print(txt_again.read())

txt.close()
txt_again.close()

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PS D:\pythonp> python ex15.3.py ex15_sample.txt
Here's your file ex15_sample.txt:
This is stuff I typed into a file.
It is really a cool stuff.
Lots and lots fun to have in here.

Type the filename again
>ex15_sample.txt
This is stuff I typed into a file.
It is really a cool stuff.
Lots and lots fun to have in here.

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知识点

open（）函数

• 语法
  open(file, mode=‘r’, buffering=-1, encoding=None, errors=None, newline=None, closefd=True)

• 运行
  打开file并返回对应的file object。若文件不能打开，则触发OSError。

  • file object——文件对象
    对外提供面向文件 API 以使用下层资源的对象（带有 read() 或 write() 这样的方法）。

• 参数

  常用的是file，mode和encoding

  • file
    file 是一个 path-like object，表示将要打开的文件的路径（绝对路径或者当前工作目录的相对路径），也可以是要被封装的整数类型文件描述符。

    • path-like object——路径类对象
      代表一个文件系统路径的对象。

    • file指定了要打开的文件名称
    • file的数据类型为字符串
    • file也包含了文件所在的存储路径，存储路径可以是相对路径，也可以是绝对路径。

  • mode

    mode指定了文件的打开模式，也就是设定文件的打开权限。

• buffering

  • buffering用于指定打开文件所用的缓冲方式。
  • 缓冲是指用于读取文件的缓冲区，缓冲区就是一段内存区域。设置缓冲区的目的是先把文件内容读取到缓冲区，可以减少CPU读取磁盘的次数。

• encoding

  • encoding用于指定文件的编码方式，默认采用utf-8，一般使用utf8或gbk。
  • 编码方式主要是指文件中的字符编码。
  • win系统默认是gbk编码的，所以桌面生成的TXT之类的都是gbk编码的

• errors

  • errors的取值一般有strict，ignore
  • 当取strict的时候，字符编码出现问题的时候，会报错
  • 当取ignore的时候，编码出现问题，程序会忽略而过，继续执行下面的程序。

• newline
  可以取的值有None, \n, \r, ‘’, ‘\r\n’ ，用于区分换行符，但是这个参数只对文本模式有效；

• closefd
  取值与传入的文件参数有关，默认情况下为True，传入的file参数为文件的文件名，取值为False的时候，file只能是文件描述符，什么是文件描述符，就是一个非负整数，在Unix内核的系统中，打开一个文件，便会返回一个文件描述符。

tips：

• file.close()

注意，当操作文件结束后，必须调用 close() 函数手动将打开的文件进行关闭，这样可以避免程序发生不必要的错误。

read()函数

• 适用文件

  • 对于借助 open() 函数，并以可读模式（包括 r、r+、rb、rb+）打开的文件，可以调用 read() 函数逐个字节（或者逐个字符）读取文件中的内容。
    • 如果文件是以文本模式（非二进制模式）打开的，则 read() 函数会逐个字符进行读取
    • 如果文件以二进制模式打开，则 read() 函数会逐个字节进行读取。

• 语法
  file.read([size])

• 参数

  • file
    表示已打开的文件对象；
  • size
    可选参数，用于指定一次最多可读取的字符（字节）个数，如果省略，则默认一次性读取所有内容。

    size 表示的是一次最多可读取的字符（或字节）数，因此，即便设置的 size 大于文件中存储的字符（字节）数，read() 函数也不会报错，它只会读取文件中所有的数据。

习题16 读写文件

from sys import argv

script, filename = argv

print(f"We're going to erase {filename}.")
print("If you don't want that, hit CTRL-C (^C).")
print("If you do want that, hit RETURN.")

input("?")

print("Opening the file...")
target = open(filename, "w")

print("Truncating the file. Goodbye!")
target.truncate()

print("Now I'm going to ask you for three lines.")

line1 = input("line 1: ")
line2 = input("line 2: ")
line3 = input("line 3: ")

print("I'm going to write these to the file.")

target.write(line1)
target.write("\n")
target.write(line2)
target.write("\n")
target.write(line3)
target.write("\n")

print("And finally, we close it.")
target.close()

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PS D:\pythonp> python ex16.py test.txt
We're going to erase test.txt.
If you don't want that, hit CTRL-C (^C).
If you do want that, hit RETURN.
?^C
Opening the file...
Truncating the file. Goodbye!
Now I'm going to ask you for three lines.
line 1: A
line 2: B
line 3: C
I'm going to write these to the file.
And finally, we close it.
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1. 如果你觉得自己没有弄懂，用我们的老办法，在每一行之前加上注释，为自己理清思路。一条简单的注释将帮你理解，或者至少让你知道自己究竞哪里没弄明白需要多下功夫。

# 将sys模块导入
from sys import argv

# 将argv解包，将参数依次赋值给左边的变量
script, filename = argv

# 打印f-字符串：我们将要擦除给定文件名内的内容
print(f"We're going to erase {filename}.")
# 打印字符串：如果你不想要这样，点击CTRL-C （^C）
print("If you don't want that, hit CTRL-C (^C).")
# 打印字符串：如果你想要这样，点击RETURN
print("If you do want that, hit RETURN.")

# 打印“？”并获得输入内容
input("?")

# 打印字符串：正在打开文件……
print("Opening the file...")
# 以只写方式打开文件并返回相应的文件对象，并将其赋值给左边的target变量
target = open(filename, "w")

# 打印字符串：删截文件。再见！
print("Truncating the file. Goodbye!")
# 清空target文件
target.truncate()

# 打印字符串：现在我要问你三句话
print("Now I'm going to ask you for three lines.")

# 打印“line 1：”，获得输入内容并将其赋值给line1
line1 = input("line 1: ")
# 打印“line 2：”，获得输入内容并将其赋值给line2
line2 = input("line 2: ")
# 打印“line 3：”，获得输入内容并将其赋值给line3
line3 = input("line 3: ")

# 打印字符串：我要将这些写入文件
print("I'm going to write these to the file.")

# 将line1写入target
target.write(line1)
# 将\n换行符写入target
target.write("\n")
# 将line2写入target
target.write(line2)
# 将\n换行符写入target
target.write("\n")
# 将line3写入target
target.write(line3)
# 将\n换行符写入target
target.write("\n")

# 打印字符串：最终，我们关闭文件
print("And finally, we close it.")
# 关闭target文件
target.close()

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2. 写一段与上一个习题类似的脚本，使用read和argv读取你刚才新建的文件。

from sys import argv

script, filename = argv

txt = open(filename)

print(txt.read())

txt.close()
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PS D:\pythonp> python ex16.1.py test.txt
A
B
C

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3. 这个文件中重复的地方太多了。试着用一个 target. write（）将1ine1、1ine2和1ine3打印出来，替换掉原来的6行代码。你可以使用字符串、格式化字符和转义字符。

from sys import argv

script, filename = argv

print(f"We're going to erase {filename}.")
print("If you don't want that, hit CTRL-C (^C).")
print("If you do want that, hit RETURN.")

input("?")

print("Opening the file...")
target = open(filename, "w")

print("Truncating the file. Goodbye!")
target.truncate()

print("Now I'm going to ask you for three lines.")

line1 = input("line 1: ")
line2 = input("line 2: ")
line3 = input("line 3: ")

print("I'm going to write these to the file.")

target.write(f"{line1} \n {line2} \n {line3} \n")

print("And finally, we close it.")
target.close()

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PS D:\pythonp> python ex16.2.py test1.txt
We're going to erase test1.txt.
If you don't want that, hit CTRL-C (^C).
If you do want that, hit RETURN.
?CTRL-C
Opening the file...
Truncating the file. Goodbye!
Now I'm going to ask you for three lines.
line 1: AA
line 2: BB
line 3: CC
I'm going to write these to the file.
And finally, we close it.
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4. 找出需要给open多传入一个’w’参数的原因。提示：open对文件的写入操作态度是安全第一，所以只有特别指定以后，它才会进行写入操作。

   确保操作完成后文件内的内容仅为本次操作写入的内容。
   若文件本身已存在，则清空文件原本内容后，从头写入本次操作写入的内容

5. 如果你用’w’模式打开文件，那么你是不是还需要 target. truncate（）呢？阅读下 Python的open函数的文档找找答案。

   不需要，理由如上条

知识点

函数

• close()
  关闭文件。跟你的编辑器中的“文件”→“保存”是一个意思。
• read()
  读取文件的内容。你可以把结果赋给一个变量。
• readline()
  只读取文本文件中的一行。
• truncate()
  清空文件，请小心使用该命令。
• write(‘stuff’)
  将“stuff”写入文件。
• seek(0)
  将读写位置移动到文件开头