Python File writelines() Method - Learn Python in simple and easy steps starting from basic to advanced concepts with examples including Python Syntax Object Oriented. The Python Writing to Files tutorial explains how to write to files using Python. And it will write it to the file following that one way process it does.

In Python, there is no need for importing external library to read and write files. Python provides an inbuilt function for creating, writing and reading files. In this tutorial, we will learn • • • How to create a Text File With Python you can create a.text files (guru99.txt) by using the code, we have demonstrated here how you can do this Step 1) f= open('guru99.txt','w+') • We declared the variable f to open a file named textfile.txt. Open takes 2 arguments, the file that we want to open and a string that represents the kinds of permission or operation we want to do on the file • Here we used 'w' letter in our argument, which indicates write and the plus sign that means it will create a file if it does not exist in library • The available option beside 'w' are 'r' for read and 'a' for append and plus sign means if it is not there then create it Step 2) for i in range(10): f.write('This is line%d r n'% (i+1)) • We have a for loop that runs over a range of 10 numbers. • Using the write function to enter data into the file. • The output we want to iterate in the file is 'this is line number', which we declare with write function and then percent d (displays integer) • So basically we are putting in the line number that we are writing, then putting it in a carriage return and a new line character Step 3) f.close() • This will close the instance of the file guru99.txt stored Here is the result after code execution When you click on your text file in our case 'guru99.txt' it will look something like this How to Append Data to a File You can also append a new text to the already existing file or the new file.

Step 1) f=open('guru99.txt', 'a+') Once again if you could see a plus sign in the code, it indicates that it will create a new file if it does not exist. But in our case we already have the file, so we are not required to create a new file. Step 2) for i in range(2): f.write('Appended line%d r n'% (i+1)) This will write data into the file in append mode. You can see the output in 'guru99.txt' file. The output of the code is that line number 1 is appended with line number 2. How to Read a File Not only you can create.txt file from Python but you can also call.txt file in a 'read mode'(r). Step 1) Open the file in Read mode f=open('guru99.txt', 'r') Step 2) We use the mode function in the code to check that the file is in open mode.

If yes, we proceed ahead if f.mode == 'r': Step 3) Use f.read to read file data and store it in variable content. Contents =f.read() Step 4) print contents Here is the output Step 5) You can also read your.txt file line by line if your data is too big to read.

This code will segregate your data in easy to ready mode When you run the code ( f1=f.readlines()) for reading the file or document line by line, it will separate each line and present the file in a readable format. In our case the line is short and readable, the output will look similar to the read mode. But if there is a complex data file which is not readable, this piece of code could be useful. Here is the complete code def main(): f= open('guru99.txt','w+') #f=open('guru99.txt','a+') for i in range(10): f.write('This is line%d r n'% (i+1)) f.close() #Open the file back and read the contents #f=open('guru99.txt', 'r') # if f.mode == 'r': # contents =f.read() # print contents #or, readlines reads the individual line into a list #fl =f.readlines() #for x in fl: #print x if __name__== '__main__': main() Summary • Python allows you to read, write and delete files • Use the function open('filename','w+') to create a file. The + tells the python compiler to create a file if it does not exist • To append data to an existing file use the command open('Filename', ' a') • Use the read function to read the ENTIRE contents of a file • Use the readlines function to read the content of the file one by one.

This chapter covers all the basic I/O functions available in Python. For more functions, please refer to standard Python documentation. Printing to the Screen The simplest way to produce output is using the print statement where you can pass zero or more expressions separated by commas.

This function converts the expressions you pass into a string and writes the result to standard output as follows − #!/usr/bin/python print 'Python is really a great language,', 'isn't it?' This produces the following result on your standard screen − Python is really a great language, isn't it? Reading Keyboard Input Python provides two built-in functions to read a line of text from standard input, which by default comes from the keyboard. These functions are − • raw_input • input The raw_input Function The raw_input([prompt]) function reads one line from standard input and returns it as a string (removing the trailing newline). #!/usr/bin/python str = raw_input('Enter your input: '); print 'Received input is: ', str This prompts you to enter any string and it would display same string on the screen. When I typed 'Hello Python!' , its output is like this − Enter your input: Hello Python Received input is: Hello Python The input Function The input([prompt]) function is equivalent to raw_input, except that it assumes the input is a valid Python expression and returns the evaluated result to you.

#!/usr/bin/python str = input('Enter your input: '); print 'Received input is: ', str This would produce the following result against the entered input − Enter your input: [x*5 for x in range(2,10,2)] Recieved input is: [10, 20, 30, 40] Opening and Closing Files Until now, you have been reading and writing to the standard input and output. Now, we will see how to use actual data files.

Python provides basic functions and methods necessary to manipulate files by default. You can do most of the file manipulation using a file object. The open Function Before you can read or write a file, you have to open it using Python's built-in open() function. This function creates a file object, which would be utilized to call other support methods associated with it. Syntax file object = open(file_name [, access_mode][, buffering]) Here are parameter details − • file_name − The file_name argument is a string value that contains the name of the file that you want to access. • access_mode − The access_mode determines the mode in which the file has to be opened, i.e., read, write, append, etc. A complete list of possible values is given below in the table.

This is optional parameter and the default file access mode is read (r). • buffering − If the buffering value is set to 0, no buffering takes place. If the buffering value is 1, line buffering is performed while accessing a file. If you specify the buffering value as an integer greater than 1, then buffering action is performed with the indicated buffer size.

If negative, the buffer size is the system default(default behavior). Here is a list of the different modes of opening a file − Sr.No. Modes & Description 1 r Opens a file for reading only.

The file pointer is placed at the beginning of the file. This is the default mode. 2 rb Opens a file for reading only in binary format.

Crash Crash Hear The Waves Go Bash here. The file pointer is placed at the beginning of the file. This is the default mode. 3 r+ Opens a file for both reading and writing.

The file pointer placed at the beginning of the file. 4 rb+ Opens a file for both reading and writing in binary format. The file pointer placed at the beginning of the file.

5 w Opens a file for writing only. Overwrites the file if the file exists.

If the file does not exist, creates a new file for writing. 6 wb Opens a file for writing only in binary format.

Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.

7 w+ Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing. 8 wb+ Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing. 9 a Opens a file for appending.

The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. 10 ab Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists.

That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. 11 a+ Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing. 12 ab+ Opens a file for both appending and reading in binary format.

The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing. The file Object Attributes Once a file is opened and you have one file object, you can get various information related to that file. Here is a list of all attributes related to file object − Sr.No. Attribute & Description 1 file.closed Returns true if file is closed, false otherwise. 2 file.mode Returns access mode with which file was opened.

3 file.name Returns name of the file. 4 file.softspace Returns false if space explicitly required with print, true otherwise. Example #!/usr/bin/python # Open a file fo = open('foo.txt', 'wb') print 'Name of the file: ', fo.name print 'Closed or not: ', fo.closed print 'Opening mode: ', fo.mode print 'Softspace flag: ', fo.softspace This produces the following result − Name of the file: foo.txt Closed or not: False Opening mode: wb Softspace flag: 0 The close() Method The close() method of a file object flushes any unwritten information and closes the file object, after which no more writing can be done. Python automatically closes a file when the reference object of a file is reassigned to another file.

It is a good practice to use the close() method to close a file. Syntax fileObject.close(); Example #!/usr/bin/python # Open a file fo = open('foo.txt', 'wb') print 'Name of the file: ', fo.name # Close opend file fo.close() This produces the following result − Name of the file: foo.txt Reading and Writing Files The file object provides a set of access methods to make our lives easier.

We would see how to use read() and write() methods to read and write files. The write() Method The write() method writes any string to an open file. It is important to note that Python strings can have binary data and not just text. The write() method does not add a newline character (' n') to the end of the string − Syntax fileObject.write(string); Here, passed parameter is the content to be written into the opened file.

Example #!/usr/bin/python # Open a file fo = open('foo.txt', 'wb') fo.write( 'Python is a great language. NYeah its great!!

N'); # Close opend file fo.close() The above method would create foo.txt file and would write given content in that file and finally it would close that file. If you would open this file, it would have following content. Python is a great language. Yeah its great!! The read() Method The read() method reads a string from an open file. It is important to note that Python strings can have binary data. Apart from text data.

Syntax fileObject.read([count]); Here, passed parameter is the number of bytes to be read from the opened file. This method starts reading from the beginning of the file and if count is missing, then it tries to read as much as possible, maybe until the end of file. Example Let's take a file foo.txt, which we created above.

#!/usr/bin/python # Open a file fo = open('foo.txt', 'r+') str = fo.read(10); print 'Read String is: ', str # Close opend file fo.close() This produces the following result − Read String is: Python is File Positions The tell() method tells you the current position within the file; in other words, the next read or write will occur at that many bytes from the beginning of the file. The seek(offset[, from]) method changes the current file position.

The offset argument indicates the number of bytes to be moved. The from argument specifies the reference position from where the bytes are to be moved. If from is set to 0, it means use the beginning of the file as the reference position and 1 means use the current position as the reference position and if it is set to 2 then the end of the file would be taken as the reference position. Example Let us take a file foo.txt, which we created above. Insyde Software Bios Download.