File handle = open ( 'file path + file name', 'mode')
example
f = open("test.txt","r",encoding = “utf-8”)
Analysis: This is due to the python files and test.txt file in the same folder, no need to write the absolute path test
If you want to write the absolute path can be written
f = open(file = "d:/python/test.txt","r",encoding = “utf-8”)
There are several files open mode mode
1, the text file open mode
"R", the default mode [read-only mode, the file must exist, there is no exception is thrown]
"W", write-only mode [unreadable; does not exist, create; there is then emptied the contents]
"A", only additional write mode [unreadable; does not exist, create; there is only the additional content]
Is opened in a binary file, the read byte is the type of content, but also a need to provide byte type writing, you can not specify the encoding
"+" Indicates a file can read and write at the same time
"R +", [reader readable, writable]
"W +", [read write read, write}
"A +", [read write read, write}
2、readable()、writable()
readable's () determines whether the file read, return True or False,
Are writable () whether a file is writable return True or False,
example
f.readable()
f.writable()
3、read()、readline() 、readlines()
f.read () # read all of the content, move the cursor to the end of file
Returns the result of a string, read([size])a method to read the file size bytes from the current position, if no size parameter, indicates to the file until the end of the reading
f.readline () # read a single line, the cursor moves to the second row header
Result is returned as a string
f.readlines () # read each line content, stored in the list
Read all text content, each line as an element of a list, and returns the results in a list format, but read large files would be more total memory.
4、write(）、writelines( ）
write () to write the string
writelines () can pass both strings and can pass a sequence of characters, and writes files in the sequence of characters. Note that you must pass a sequence of characters, it can not be a sequence of numbers.
f.write ( '1111 \ n222 \ n ') # write for text mode, you need to write their own newline
f.write ( '1111 \ n222 \ n'.encode (' utf-8 ')) # mode for b write, write their own needs newline
f.writelines ([ '333 \ n' , '444 \ n']) # file mode
f.writelines ([bytes ( '333 \ n', encoding = 'utf-8'), '444 \ n'.encode (' utf- 8 ')]) #b mode
5, f.close () # close the file f.closed () # to view the file is closed
After opening the file with the open method, you must use f.close () closes the file
After the file must be closed after use, because the file object will occupy the resources of the operating system and the operating system at the same time the number of files that can be opened is limited.
Whether f.closed () # View the file is closed, return True or False
6, with open as f open method
This opens the file the way to close the file without writing f.closed
example
with open('/path/to/file', 'r') as f:
with open("test.txt","r",encoding = “utf-8”) as f:
7, for non-text files, we can only use the b mode
Non-text files open mode, only the mode b, "b" represents the manner in bytes (and all the files are stored in the form of bytes, the use of this model without considering the character of the encoded text document, jgp format image files, avi format video files, b mode cross-platform)
"rb"
"wb"
"ab"
f = open("test.py","rb")
Analysis: Note that this can not be applied, encoding = "utf-8", because there is a binary opened, do not need to set the encoding open
example
f = open("test.py","rb")
data = f.read()
print(data)
test.py contents of the file:
Export
b'"111"\r\n"2222"\r\n"3333"\r\n\xe4\xbd\xa0\xe5\xa5\xbd'
Analysis: Here \ r \ n is the newline Windows platform, beginning with b represents the output byte form
Here \ xe4 \ xbd \ xa0 \ xe5 \ xa5 \ xbd 'on behalf of Chinese characters
f = open("test.py","rb")
data = f.read()
print(data.decode("utf-8"))
Output
"111" "2222" "3333" 你好
Analysis: as used herein when test.py file storage utf-8 is stored, to "utf-8" to be decoded at the time of output printout.
When opened by b, the read byte is the type of content, but also a need to provide byte type writing, you can not specify the encoding
Example 2
f = open("test11.py","wb")f.write("111\n")
f.close()
Output: Error, suggesting bytes needed here, instead of a string of bytes written here must be written in the form
Can be changed
f = open("test11.py","wb")
f.write(bytes("111\n",encoding="utf-8"))
f.close()
Analysis: here you can string "111 \ n" is written files, where bytes () must be assigned a code.
Or directly encoded string, not bytes () method
f = open("test11.py","wb")
f.write("222\n".encode("utf-8"))
f.close()
8、f.encoding
Take open files encoded
example
f = open("test11.py","w",encoding="gbk")
f.write("222\n")
f.close()
print(f.encoding)
Export
gbk
Analysis: where the file is open coding that open statements in the code, regardless of the actual encoding of the source file.
9、f.flush() 、f.tell()
f.flush () immediately file contents from memory to the hard brush, where the need to use the command prompt operation, will be written directly to write the contents of the hard disk pycharm years, do not need to flush ()
f.tell () Gets the current cursor position
10, the cursor moves in the paper
read(3)：
When a, as a way to open the file in text mode, read on behalf of three characters
B, the file open mode is a mode b, three bytes represent the data read
read () reads the entire file default
The remaining files are cursor movement bytes as seek, tell, truncate
example
test.txt file contents
f = open("test.txt","rb")
data = f.read(6)
f.close()
print(data)
Output
b'111 \ r \ n2 '
Analysis: This 3-byte count 111, \ r \ n 2 byte count, a byte count 2, where b is the mode for calculation byte, i.e. there can not specify the encoding can not be written encoding = "xx ", otherwise it will error
Example 2
File contents same as above
f = open("test.txt","r+",encoding="utf-8")
data = f.read(6)
f.close()
print(data)
Output
111 22
Analysis: This is a text mode, where the operator 3 111, newline \ r \ n a character count, count 2 22 characters, a total of six characters.
11、seek()
seek () move the cursor to the file to the specified location.
seek () syntax
f.seek(offset[, whence])
i.e., the number of bytes offset movement, 0,1,2 The whence there are three modes, 0 represents the beginning of the file count, count represents the current position, represents the start end of the file count, the default is 0. 1 and 2 wherein the b mode must be carried out, but no matter what the wrap mode, the mobile units are in bytes of, the Widnows system size is two bytes (\ r \ n).
example
test.txt file contents
f = open("test.txt","r+",encoding="utf-8")
f.seek(3,0)
data = f.read()
f.close()
print(data)
Output
222 333 Hello 444 aaa bbb ccc 555
Example 2
File contents same as above
f = open("test.txt","rb")
f.seek(5)
f.seek(11,1)
print(f.tell())
data = f.read()
f.close()
print(data)
Output
16 b'\xbd\xa0\xe5\xa5\xbd\r\n444\r\naaa\r\nbbb\r\nccc\r\n555'
analysis
Here in binary open, three-byte count 111, behind unseen \ r \ n newline, therefore, seek (5) the position of the first row is the last
seek(11,1)是从当前位置继续移动光标，即222\r\n算5个字节，同理333\r\n算5个字节，“你好”(文本文件是utf-8编码的)算6个字节，因此这时只取“你”这个字的3个字节的第一个字节，光标移动到你的第一个字节之后，所以最后输出了\xbd\xa0\xe5\xa5\xbd共5个字节。
注意这里的光标操作要用seek()方法，直接用鼠标移动光标是无效的。
例子3
文件内容
f = open("test.txt","rb")
offs = -20
while True:
f.seek(offs,2)
data = f.readlines()
if len(data) > 1:
print("文件的最后一行是%s"%data[-1].decode("utf-8"))
breakf = open("test.txt","rb")
offs = -20
while True:
f.seek(offs,2)
data = f.readlines()
if len(data) > 1:
print("文件的最后一行是%s"%data[-1].decode("utf-8"))
break
这里目的是在不知道一行是多少字节的情况下输入最后一行
输出结果
文件的最后一行是2018-04-15 nicholas 学习了520分钟
分析：seek(-20,2)是从文件的最后开始计算的，必须以b模式进行。
12、 truncate()
truncate() 方法用于从文件的首行首字节开始截断，截断文件为 size 个字节，无 size 表示从当前位置截断；截断后面的所有字节被删除，其中 Widnows 系统下的换行代表2个字节大小。
例子
文件内容
f = open("test.txt","r+")
f.truncate(10)
data = f.read()
print(data)
输出结果
111 aaa