Python StringIO 模块

2024 年 8 月 29 日 | 阅读 6 分钟

StringIO 模块是一个内存中的类文件对象。它可以用于输入或输出用户可以从普通文件对象期望的大部分函数。用户创建 StringIO 对象后，它最初是通过向构造函数提供一个字符串来创建的。如果没有字符串，StringIO 将为空。在这两种情况下，文件上的初始光标都将从零开始。

该模块在最新版本的 Python 中不可用；因此，要使用此模块，我们需要将其转移到 Python 的 Io 模块中，形式为 io.StringIO。

示例

# First, we will import the required module.
from io import StringIO as SIO


# The arbitrary string.
string_1 = 'This is the initialized string.'

# Here, we will use the StringIO method for setting as the file object. 
# Now, we have an object-file that we can treat as a file.
file_1 = SIO(string_1)

# Now, we will be reading the file by using read()
print (file_1.read())

# Here, We can also write in this file.
file_1.write(" Welcome to Javatpoint.com.")

# by using the following command,  we can make the cursor at index 0.
file_1.seek(0)

# by using the following command, the user is able to print the file after writing #in the initialized string (string_1).
print ('The file of the string after writing in it is:', file_1.read())

输出

This is the initialized string.
The file of the string after writing in it is: This is the initialized string. Welcome to Javatpoint.com.

StringIO 的重要方法

以下是 StringIO 的一些方法

1. StringIO.getvalue(): 此函数用于返回文件的全部内容。

语法

上述方法的语法是

示例

# First, we will import the StringIO module.
from io import StringIO as SIO

# The arbitrary string.
string_1 = 'Hello and thank you for visiting to Javatpoint.com.'

# Here, we will use the StringIO method for setting as the file object.
file_1 = SIO(string_1)

# Retrieving the complete contents of the above file.
print(file_1.getvalue())

输出

Hello and thank you for visiting to Javatpoint.com

2. 在这里，我们查看 StringIO 的一些返回布尔值（即 false 或 true）的函数

isatty(): StringIO 的此函数在流不可交互时返回 False，在流可交互时返回 True。
readable(): StringIO 的此函数在文件不可读时返回 False，在文件可读时返回 True。
writable(): StringIO 的此函数在文件不支持写入时返回 False，在文件支持写入时返回 True。
seekable(): StringIO 的此函数在文件不支持随机访问时返回 False，在文件支持随机访问时返回 True。
closed: StringIO 的此函数在文件打开时返回 False，在文件关闭时返回 True。

语法

上述方法的语法是

File_name.isatty()
File_name.readable()
File_name.writable()
File_name.seekable()
File_name.closed

示例

# First, we will import the StringIO module.
from io import StringIO as SIO

# The arbitrary string.
string_1 = 'Hello and thank you for visiting to Javatpoint.com.'

# Here, we will use the StringIO method for setting
# as the file object.
file_1 = SIO(string_1)

# by using the following command,  the user will be able to return is the file #interactive or not.
print ("Is the file stream above interactive?", file_1.isatty())

# by using the following command, 
# the user will be able to return is the file readable or not.
print ("Is the file stream above readable?", file_1.readable())

# by using the following command, 
#  the user will be able to return does the file support writing or not.
print ("Is the file stream above writable?", file_1.writable())

# by using the following command, ,  the user will be able to return is the file #seekable or not.
print ("Is the file stream above seekable?", file_1.seekable())

# by using the following command,  the user will be able to return is the file #closed or not.
print ("Is the file above closed?", file_1.closed)

输出

Is the file stream above interactive? False
Is the file stream above readable? True
Is the file stream above writable True
Is the file stream above seekable? True
Is the file above closed? False

3. StringIO.seek(): seek() 函数用于设置文件内光标的位置。如果我们对文档执行任何写入或读取操作，光标将放置在使用过的最后一个索引上，以便我们可以使用 seek() 将光标从文件的起始位置移动。

语法

上述方法的语法是

File_name.seek(argument) 
#This argument tells the function where to place the cursor.

示例

# First, we will import the StringIO module.
from io import StringIO as SIO

# The arbitrary string.
string_1 ='Hello and thank you for visiting to Javatpoint.com.'

# Here, we will use the StringIO method for setting as the file object.
file_1 = SIO(string_1)

# here, the user will be able to Read the file:
print (file_1.read())

#If the user wishes to view the file again, it will display empty file since the #cursor has been set to the last index. It will also not print anything because #the function returns an empty string.
print (file_1.read())

#  So, to set the cursor position for reading or writing the file again
# we can use seek() function. 
#We can pass any index here form(0 to len(file))
file_1.seek(0)

# Now the user can read the file again
print (file_1.read())S

输出

Hello and thank you for visiting to Javatpoint.com.

Hello and thank you for visiting to Javatpoint.com.

4. StringIO.truncate(): 此函数用于调整文件流的大小。此方法会保存文件并删除给定索引之后的内容。

语法

上述方法的语法是

File_name.truncate(size = None)
# The user can provide the size from where to truncate the file.

示例

# First, we will import the StringIO module.
from io import StringIO as SIO

# The arbitrary string.
string_1 ='Hello and welcome to Javatpoint.com.'

# Here, we will use the StringIO method for setting as the file object.
file_1 = SIO(string_1)
# here, we can read the initial file:
print(file_1.read())

# for setting the cursor at 0.
file_1.seek(0)


# for dropping the file after the given index, i.e., 14.
file_1.truncate(14)

# here, it will print the File after truncate.
print(file_1.read())

输出

Hello and welcome to Javatpoint.com.
Hello and welc

5. StringIO.tell(): 此方法用于获取文件的当前流和光标位置。

语法

上述方法的语法是

示例

# First, we will import the StringIO module.
from io import StringIO as SIO

# The arbitrary string.
string_1 ='Hello and welcome to Javatpoint.com.'

# Here, we will use the StringIO method for setting as the file object.
file_1 = SIO(string_1)

# Here the cursor is set at index '0'.
print(file_1.tell())

# now, we are setting the Cursor to index '23'.
file_1.seek(23)

# here, we will be printing the index of cursor
print(file_1.tell())

输出

0
23

6. StringIO.close() 用于关闭文件。此函数在一个文件上调用，我们无法对其执行任何操作。任何操作都会导致 ValueError。

语法： =

上述方法的语法是

示例

# First, we will import the StringIO module.
from io import StringIO as SIO

# The arbitrary string.
string_1 ='Hello and welcome to Javatpoint.com.'

# Here, we will use the StringIO method for setting as the file object.
file_1 = SIO(string_1)

# here, we can read the initial file:
print(file_1.read())

# for closing the current file.
file_1.close()

# If the user would perform any operation on the above file now, it will raise an #ValueError.

# here, we will be using the closed function to know whether the file is closed #or not.
print("Is the file closed?", file_1.closed)

输出

Hello and welcome to Javatpoint.com.
Is the file closed? True

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