R Read Txt Content Truncated by ;
In this tutorial we volition larn to work with files then your programs tin quickly analyze lots of information. We will primarily use with open() function to create, read, append or write to file using Python programming linguistic communication.
Below are the listing of topics nosotros volition cover in this tutorial:
- How to create an empty file
- How to read the content of a text file
- How to write to a file
- How to append new content to an existing file
How would yous write to a file in GUI Surroundings?
Let us sympathize in a very basic laymen terms. As most of you I assume have an experience of windows environs, to write to a file in some notepad with graphical interface, what would you lot do?
- Create a new text file (if not already nowadays)
- Open the file for editing
- Write your information into the file
- Save the file
- Shut the file once washed
We follow something similar arroyo in Python when working with text files to perform read/write operations.
Syntax to open files with the open() function
To open a file with the open() role, you pass it a string path indicating the file you want to open; it can be either an absolute or relative path.
Syntax i: Using with open()
The syntax to open up a file in Python would be:
with open('<PATH/OF/FILE>','<MODE>') as <FILE_OBJECT>: - The
open()part needs one argument: the name of the file you want to open. - Python looks for this file in the directory where the programme that'south currently being executed is stored.
- So information technology is recommended to utilize accented or relative path for the provided file.
- The open() role returns a
FILE_OBJECTwhich represents the file. ThisFILE_OBJECTtin can be any variable as per your selection. - Next yous must assign a
Fashionto open the file.
You lot can choose from the beneath available modes in Python:
You lot likewise have an pick to open up the file in:
- Text mode ("t")
- Binary mode ("b")
HINT:
So if you wish to open a file in write + binary fashion then you lot should give " wb ". By default open() will open the file in text mode so you need not provide "<strong>t</strong>" every time you lot use open() for text files.
Syntax ii: Using open() and close()
- Alternatively we can likewise open a file by directly using the
open()part and assigning information technology toFILE_OBJECT - This
FILE_OBJECTcan over again exist whatsoever variable. - We tin use the same set of modes in the aforementioned format as we discussed above.
- The only deviation hither is that we must provide
shut()function in one case we are washed working with the file
FILE_OBJECT = open('<PATH/OF/FILE>','<MODE>') # read write operations FILE_OBJECT.shut()
Which syntax should I employ (with open() or open())?
- The keyword
close()closes the file once access to information technology is no longer needed. - You must take noticed, using "
with" how we phone callopen()in this program merely notshut(). - Y'all could open and shut the file by calling
open()andclose()office respectively, but if a bug in your program prevents theclose()method from being executed, the file may never close. - This may seem little, simply improperly closed files can crusade information to be lost or corrupted.
- And if y'all call
close()too early in your program, you'll notice yourself trying to piece of work with a closed file (a file you can't access), which leads to more errors. - It's not always easy to know exactly when you lot should close a file, merely
with open()python will effigy that out for you lot. - All you have to do is open up the file and work
withit as desired, trusting that Python volition close it automatically when the with cake finishes execution.
How to create an empty file
Example 1: Using touch()
Ideally if your intention is simply to create an empty file, you can utilize touch() function as shown below or subprocess.call with touch command:
#!/usr/bin/env python3 from pathlib import Path Path('/tmp/file.txt').impact()
This will create an empty file nether /tmp/
# python3 file_operator.py
Verify if the new file was created:
# ls -l /tmp/file.txt -rw-r--r-- 1 root root 0 Jul xix eleven:08 /tmp/file.txt Example 2: Using with open up()
Only since this tutorial is about open() and with open(), we volition utilise these functions in combination with different manner to create an empty file. Adjacent we will utilise with open() equally shown below. Here I am using file_object every bit the variable name for FILE_OBJECT, you tin use whatever other variable.
#!/usr/bin/env python3 with open('/tmp/file.txt', 'x') equally file_object: laissez passer
Here we will create /tmp/file.txt using "x" which ways create an empty file.
Execute the script:
This script fails with error "File exists".
Annotation:
Using "10" with open() nosotros can create an empty file only if the file is not present. If the provided file is already present, the create performance volition fail.
And so we will delete our exiting /tmp/file.txt and re-execute the script:
# rm -f /tmp/file.txt
# python3 file_operator.py
And so the new file is created now.
# ls -l /tmp/file.txt -rw-r--r-- 1 root root 0 Jul 19 eleven:15 /tmp/file.txt Example three: Using open up()
Nosotros can too utilize open() office in this format:
#!/usr/bin/env python3 file_object = open('/tmp/file.txt', '10') file_object.shut()
and this will also go ahead and create an empty file /tmp/file.txt (if not present already)
How to read the contents of file
Now that you have a File object, you can beginning reading from it. There can be different ways to read the content of file which we will larn in this section with different examples:
The basic syntax to read the content of a file would be:
with open('<PATH/OF/FILE>','r') as <FILE_OBJECT>: FILE_OBJECT.read() OR
FILE_OBJECT = open('<PATH/OF/FILE>','r') FILE_OBJECT.read() Here nosotros use "<potent>r</strong>" i.e. read mode with open up() role. To actually read the content we demand to utilize read() with our file object value.
In the below examples, I will use this dataFile to test our read() performance.
# cat dataFile some appointment-1 five some information-2 10 some data-iii xv Example ane: Read the content of a file as string
If you desire to read the unabridged contents of a file as a string value, apply the File object'due south read() method.
#!/usr/bin/env python3 # Open up the file in read mode file_object = open up('dataFile', 'r') # Store the content of file in content var. # You tin can use whatsoever name for this variable content = file_object.read() # print the content print(content) # Close the file object of file file_object.close()
Execute the script:
# python3 file_operator.py some date-i 5 some data-ii 10 some data-3 fifteen NOTE:
You may discover an extra new line grapheme in the output of this script compared to the original file. The blank line appears because read() returns an empty string when it reaches the end of the file; this empty string shows up as a blank line. If yous want to remove the extra bare line, you can use rstrip() in the call to impress():
So, to remove the newline from the last line, our code would expect similar:
#!/usr/bin/env python3 # Open the file in read fashion file_object = open('dataFile', 'r') # Store the content of file in content var. # You can apply whatever name for this variable content = file_object.read() # impress the content print(content.rstrip()) # Close the file object of file file_object.close()
Now this should non give any extra new line at the end of the print output.
Similarly to use with open() function
#!/usr/bin/env python3 # Open up the file in read mode with open('dataFile', 'r') as file_object: # Shop the content of file in content var. # You can use whatever proper name for this variable content = file_object.read() # print the content print(content.rstrip())
Output from this script:
# python3 file_operator.py some date-1 5 some data-2 10 some data-3 15 Example two : Read content of the file line by line
When y'all're reading a file, you lot'll oftentimes want to examine each line of the file. Yous might be looking for sure information in the file, or you might want to alter the text in the file in some way.
- Y'all can use a
forloop on the file object to examine each line from a file one at a time - In this example we assign the file with it's path to
filenamevariable - We again use the
withsyntax to let Python open and shut the file properly. - To examine the file's contents, we work through each line in the file past looping over the file object
#!/usr/bin/env python3 filename = '/root/scripts/dataFile' # Open the file in read mode with open(filename, 'r') as file_object: for line in file_object: print(line)
Output from this script. When we print each line, we discover even more than blank lines. These bare lines appear because an invisible newline grapheme is at the end of each line in the text file. The print function adds its ain newline each time we call information technology, and then we cease up with two newline characters at the end of each line, one from the file and one from impress().
# python3 file_operator.py some engagement-i 5 some information-2 10 some data-3 15 Using rstrip() on each line in the print() call eliminates these actress blank lines. Updated script using rstrip()
#!/usr/bin/env python3 filename = '/root/scripts/dataFile' # Open the file in read manner with open(filename, 'r') as file_object: for line in file_object: impress(line.rstrip())
Output from this script:
# python3 file_operator.py some date-1 5 some data-ii 10 some data-3 xv Example iii - Store the content from a file in List (readlines())
- When you apply with, the file object returned by
open up()is but available inside the with block that contains it. - If yous want to retain access to a file's contents outside the with block, you can shop the file'south lines in a listing inside the block and and then work with that list.
- Y'all can process parts of the file immediately and postpone some processing for later on in the program.
#!/usr/bin/env python3 filename = '/root/scripts/dataFile' # Open the file in read fashion and store the content in file_object with open(filename, 'r') as file_object: # Use readlines() to shop the content in lines variable as a List lines = file_object.readlines() # Apply for loop exterior the scope of with open() and # impress the content of lines for line in lines: print(line.rstrip())
Output from this script:
# python3 file_operator.py some date-1 5 some data-2 10 some data-3 15 Example iv - Perform uncomplicated calculation
Now when we know how to read a file in python, let's utilise this to perform some bones addition. In this script we will calculate the third column value and print the full. I have already explained each line in the script's comment section
filename = '/root/scripts/dataFile' total = 0.0 # Open up the file in write mode and store the content in file_object with open(filename, 'r') as file_object: for line in file_object: # Split the line based on whitespace character parts = line.split up( ) # Convert the value into integer of 3rd cavalcade parts[2] = int(parts[2]) # Add all the values from 3rd column total += parts[ii] # Print the total print(full)
The output from this script:
# python3 file_operator.py 30.0 Instance five: Read and align the data using format
In this example we volition read the content from our dataFile and using print format, we will align the content of this file. I have added enough comments to explicate each line of the lawmaking.
#!/usr/bin/env python3 filename = '/root/scripts/dataFile' # Open the file in write way and shop the content in file_object with open(filename, 'r') equally file_object: # This department would be executed only if with is successful # Print a formatted cord with Offset and Second is left aligned with a value of 10 # and Tertiary is right aligned with a value of five print(f'{"Outset":<10}{"Second":<x}{"Third":>5}') for line in file_object: # Split the line based on whitespace character parts = line.split( ) # Adapt the line content with the provided format # as we had used earlier for alignment print(f'{parts[0]:<10}{parts[1]:<10}{parts[2]:>five}')
Snippet of the script from my final:
Output from this script:
How to write to file
- To write text to a file, you lot demand to call open() with a second statement "
w" i.e. write mode telling Python that you desire to write to the file. - You should utilize "
<strong>due west</potent>" charily because it will overwrite the existing content of the file. - If the provided file is non nowadays, "
w" volition create a new file and start writing to this file - If the file is already nowadays with some data, "
w" will overwrite the content and and so write information to this file.
Case 1 : Writing to an empty file
We can use either open() or with open up(), since with open up() is more flexible and modern I will employ just this for all my examples. But I hope you lot have understood the syntax of open() so yous can port them appropriately.
In this example we will create a new file (/tmp/someData.txt) and put some content into this file
#!/usr/bin/env python3 filename = '/tmp/someData.txt' # Open up the file in write mode and store the content in file_object with open(filename, 'w') as file_object: file_object.write("Python write to file\n")
Execute this script:
# python3 file_operator.py
As expected, this plan has no final output, but you tin check if /tmp/someData.txt is created and verify the content:
# cat /tmp/someData.txt Python write to file NOTE:
Python tin only write strings to a text file. If you lot want to store numerical information in a text file, you lot'll have to convert the information to string format commencement using the str() part.
Example 2: Write multiple lines
If you lot notice the previous example, I take added "\n" to stop of the print string. The write() function doesn't add together any newlines to the text you write. Then if you write more than one line without including newline characters, your file may non expect the manner y'all want information technology to. Then we volition use "\n" new line character to write multiple lines to our text file.
#!/usr/bin/env python3 filename = '/tmp/someData.txt' # Open up the file in write mode and store the content in file_object with open(filename, 'w') as file_object: file_object.write("Start line\n") file_object.write("Second line\n")
Execute the script and observe the content of /tmp/someData.txt
# cat /tmp/someData.txt First line Second line Example 3: Perform search and modify the content of file
In this example we will perform some search then alter the content of the file which nosotros volition so store into separate file. We already have a dataFile with below content
# cat /root/scripts/dataFile some engagement-ane five some data-2 10 some data-3 15 We wish to supplant the value "10" to "20" in the 2d row of third column then we will utilise read and write method with open() function and write the updated content in a new file /tmp/temp_file.txt
#!/usr/bin/env python3 in_f = '/root/scripts/dataFile' out_f = '/tmp/temp_file.txt' # Open the file in read style and store the content in input_f input_f = open(in_f, 'r') # Open up the file in write manner and shop the content in output_f output_f = open up(out_f, 'w') # Admission both the files using with with input_f, output_f: # Run a loop for each line in the input file for line in input_f: # Split up the content using whitespace grapheme and store each field in get-go, second and third outset, 2d, third = line.carve up( ) # If 3rd column doesn't contain 10 and so only add the line in output file if third != 'ten': output_f.write(line) else: # if third column contains 10, and so replace the whole line # with provided list new_line = ' '.join([outset, 2d, 'twenty']) # Add a new line at the end of in a higher place Listing output_f.write(new_line + "\due north")
Output from this script:
# cat /tmp/temp_file.txt some engagement-one 5 some data-2 20 some data-iii 15 So our 3rd column from the second row is properly updated with the new value "20"
HINT:
You lot can perform search and replace in the aforementioned file using fileinput which is currently not in the scope of this tutorial. I may write another tutorial on this topic.
How to append content to a file
- If you want to add together content to a file instead of writing over existing content, you tin can open the file in append mode.
- When you lot open a file in
suspendmode, Python doesn't erase the contents of the file before returning the file object. - Any lines you write to the file will exist added at the terminate of the file.
- If the file doesn't exist however, Python will create an empty file for you.
Example 1: Append data to existing file
Nosotros will use our existing /tmp/someData.txt to add new line use open and " a " i.eastward. append style.
#!/usr/bin/env python3 filename = '/tmp/someData.txt' # Open the file in suspend mode and suspend the new content in file_object with open(filename, 'a') as file_object: file_object.write("Third line\north")
Nosotros execute this script and verify the content of /tmp/someData.txt
# python3 file_operator.py
The "Third line" is appended to our existing file
# cat /tmp/someData.txt Beginning line Second line Third line Appending vs Writing
If a file contains data already, and you open it in write fashion, and then write more to it, your new content will really overwrite (replace) whatever is already in the file. At that place is no undo for this. And so if the content of the file is important, y'all want to make sure you don't make that mistake. To add content to a file, open up the file in append (a) mode, then use .write to write to a file.
Conclusion
In this tutorial we learned about dissimilar text manipulation using open up() role to create, read, write and append information to a file. Yous tin can combine these modes with binary to also perform seek operation on the text file. I accept shared various examples to sympathise the different modes related to the open() function. We besides learned the departure of open() and with open() and when should yous choose which function.
Lastly I hope the steps from the article to create, read, write to file in Python programming was helpful. So, let me know your suggestions and feedback using the comment section.
Source: https://www.golinuxcloud.com/python-write-to-file/
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