Python File readline() 方法从文件中读取一整行。此方法在 read 行的末尾附加一个尾随换行符 ('\n')。
readline() 方法还接受一个可选参数,可以在其中指定要从包含换行符的行中读取的字节数。默认情况下,此可选参数将为 0,因此读取整行。
仅当立即遇到 EOF 时,才会返回空字符串。
注意:如果文件以普通读取模式打开,该方法以字符串形式返回该行。 如果文件以二进制读取模式打开,该方法将返回二进制对象。
语法
以下是 Python 文件 readline() 方法的语法 -
fileObject.readline(size);
参数
- size − 这是要从文件中读取的字节数。
返回值
此方法返回从文件中读取的行。
例让我们使用现有文件 “foo.txt” 通过 Python File readline() 方法从中读取一行。foo.txt 文件中的内容如下 -
This is 1st line
This is 2nd line
This is 3rd line
This is 4th line
This is 5th line
This is 2nd line
This is 3rd line
This is 4th line
This is 5th line
以下示例显示了上述演示文件中 readline() 方法的用法。
# Open a file
fo = open("foo.txt", "r+")
print("Name of the file: ", fo.name)
# Assuming file has following 5 lines
# This is 1st line
# This is 2nd line
# This is 3rd line
# This is 4th line
# This is 5th line
line = fo.readline()
print("Read Line:", line)
# Close opened file
fo.close()
当我们运行上述程序时,它会产生以下结果——
Name of the file: foo.txt
Read Line: This is 1st line
Read Line: This is 1st line
例
但是如果我们传递一些值作为可选参数 size,该方法最多只读取给定的字节并在末尾附加换行符。
# Open a file
fo = open("foo.txt", "r+")
print("Name of the file: ", fo.name)
# Passing the size argument to the readline() method
line = fo.readline(5)
print("Read Line:", line)
# Close opened file
fo.close()
如果我们编译并运行上面的程序,结果会产生如下 -
Name of the file: foo.txt
Read Line: This
Read Line: This
例
现在,如果文件以读取二进制模式 (rb) 打开,该方法将返回二进制对象。
我们使用 open() 函数在读取二进制模式 (rb) 中打开一个现有文件 “foo.txt”。在 open() 方法返回的文件对象上调用 readline() 方法,以二进制形式获取作为文件一行的返回值。
# Open a file
fo = open("foo.txt", "rb")
print("Name of the file: ", fo.name)
line = fo.readline()
print("Read Line:", line)
# Passing the optional parameter
line = fo.readline(5)
print("Read Line:", line)
# Close opened file
fo.close()
编译并运行程序后,输出显示如下 -
Name of the file: foo.txt
Read Line: b'This is 1st line\r\n'
Read Line: b'This '
Read Line: b'This is 1st line\r\n'
Read Line: b'This '
例
即使 size 参数大于当前文件中的行长度,该方法也仅返回整行。
# Open a file
fo = open("foo.txt", "r")
print("Name of the file: ", fo.name)
line = fo.readline(40)
print("Read Line:", line)
# Close opened file
fo.close()
让我们编译并运行给定的程序,输出显示如下 -
Name of the file: foo.txt
Read Line: This is 1st line
Read Line: This is 1st line