Python中的StringIO模块

StringIO模块是一个内存中的类似文件的对象。该对象可用作大多数需要标准文件对象的函数的输入或输出。创建 StringIO 对象时，它通过将字符串传递给构造函数进行初始化。如果没有传递字符串，则 StringIO 将开始为空。在这两种情况下，文件上的初始光标都从零开始。

注意：这个模块在最新版本的Python中不存在，所以要使用这个模块，我们必须从Python的io 模块中将它作为 io.StringIO 导入。

例子：

Python3

# Importing the StringIO module.
from io import StringIO 
 
 
# The arbitrary string.
string ='This is initial string.'
 
# Using the StringIO method to set
# as file object. Now we have an
# object file that we will able to
# treat just like a file.
file = StringIO(string)
 
# this will read the file
print(file.read())
 
# We can also write this file.
file.write(" Welcome to geeksforgeeks.")
 
# This will make the cursor at
# index 0.
file.seek(0)
 
# This will print the file after
# writing in the initial string.
print('The string after writing is:', file.read())

输出：

This is initial string. 
The string after writing is: This is initial string. Welcome to geeksforgeeks.

StringIO 的一些重要方法如下：

1. StringIO.getvalue()：该函数返回文件的全部内容。

句法：

File_name.getvalue()

例子：

Python3

# Importing the StringIO module.
from io import StringIO 
 
 
# The arbitrary string.
string ='Hello and welcome to GeeksForGeeks.'
 
# Using the StringIO method to
# set as file object.
file = StringIO(string)
 
# Retrieve the entire content of the file.
print(file.getvalue())

输出：

'Hello and welcome to GeeksForGeeks.'

2.在本文中，我们讨论 StringIO 的一些函数，它们返回布尔值，即 True 或 false：

• StringIO.isatty()：此函数如果流是交互式的，则返回 True，如果流不是交互式的，则返回 False
• StringIO.readable()：如果文件可读，此函数返回 True，如果文件不可读，则返回 False。
• StringIO.writable()：如果文件支持写入，此函数返回 True，如果文件不支持写入，则返回 False。
• StringIO.seekable()：如果文件支持随机访问，此函数返回 True，如果文件不支持随机访问，则返回 False。
• StringIO.closed：如果文件关闭，此函数返回 True，如果文件打开，则返回 False。

句法：

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

例子：

Python3

# Importing the StringIO module.
from io import StringIO 
 
 
# The arbitrary string.
string ='Hello and welcome to GeeksForGeeks.'
 
# Using the StringIO method to
# set as file object.
file = StringIO(string)
 
# This will returns whether the file
# is interactive or not.
print("Is the file stream interactive?", file.isatty())
 
# This will returns whether the file is
# readable or not.
print("Is the file stream readable?", file.readable())
 
# This will returns whether the file supports
# writing or not.
print("Is the file stream writable?", file.writable())
 
# This will returns whether the file is
# seekable or not.
print("Is the file stream seekable?", file.seekable())
 
# This will returns whether the file is
# closed or not.
print("Is the file closed?", file.closed)

输出：

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

3.StringIO.seek()： seek()函数用于设置光标在文件上的位置。如果我们对文件执行任何读写操作，则光标将设置在最后一个索引上，因此使用 seek() 将光标移动到文件的起始索引处。

句法：

File_name.seek(argument) 
# Here the argument is passed to tell the 
# function  where to set the cursor position. 

例子：

Python3

# Importing the StringIO module.
from io import StringIO 
 
 
# The arbitrary string.
string ='Hello and welcome to GeeksForGeeks.'
 
# Using the StringIO method
# to set as file object.
file = StringIO(string)
 
# Reading the file:
print(file.read())
 
# Now if we again want to read
# the file it shows empty file
# because the cursor is set to
# the last index.
 
 
# This does not print anything
# because the function returns an
# empty string.
print(file.read())
 
# Hence to set the cursor position
# to read or write the file again
# we use seek().We can pass any index
# here form(0 to len(file))
file.seek(0)
 
# Now we can able to read the file again()
print(file.read())

输出：

Hello and welcome to GeeksForGeeks.
Hello and welcome to GeeksForGeeks.

4.StringIO.truncate()：该函数用于调整文件流的大小。此方法在提供的索引之后删除文件并保存。

句法：

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

例子：

Python3

# Importing the StringIO module.
from io import StringIO 
 
 
# The arbitrary string.
string ='Hello and welcome to GeeksForGeeks.'
 
# Using the StringIO method
# to set as file object.
file = StringIO(string)
 
# Reading the initial file:
print(file.read())
 
# To set the cursor at 0.
file.seek(0)
 
 
# This will drop the file after
# index 18.
file.truncate(18)
 
# File after truncate.
print(file.read())

输出：

Hello and welcome to GeeksForGeeks.
Hello and welcome 

5.StringIO.tell()：该方法用于告诉文件当前的流或光标位置。

句法：

File_name.tell()

例子：

Python3

# Importing the StringIO module.
from io import StringIO 
 
 
# The arbitrary string.
string ='Hello and welcome to GeeksForGeeks.'
 
# Using the StringIO method to
# set aas file object.
file = StringIO(string)
 
# Here the cursor is at index 0.
print(file.tell())
 
# Cursor is set to index 20.
file.seek(20)
 
# Print the index of cursor
print(file.tell())

输出：

0
20

6.StringIO.close()：该方法用于关闭文件。对文件调用此函数后，我们无法对文件执行任何操作。如果执行任何操作，它将引发 ValueError。

句法：

File_name.close()

例子：

Python3

# Importing the StringIO module.
from io import StringIO 
 
 
# The arbitrary string.
string ='Hello and welcome to GeeksForGeeks.'
 
# Using the StringIO method to
# set as file object.
file = StringIO(string)
 
# Reading the file.
print(file.read())
 
# Closing the file.
file.close()
 
# If we now perform any operation on the file
# it will raise an ValueError.
 
# This is to know whether the
# file is closed or not.
print("Is the file closed?", file.closed)

输出：

Hello and welcome to GeeksForGeeks.
Is the file closed? True