Python append one file to another

This python program involves appending contents from one text file to another. To achieve this, let’s briefly go over python’s open() function.

This is used to open a file. It returns an object of the file type. If the file can’t be opened, IOError exception is raised. When opening a file, it’s preferable to use open() instead of invoking the file constructor directly. The first 2 arguments are the same as stdio’s fopen(). The name is the file name to be opened, and the mode is a string indicating how the file is to be opened.

Here I’m using the append mode. To achieve this we should open the file in append mode by setting ‘a’ or ‘ab’ as the mode. When we open the file with ‘a’ mode, the write position will always be at the end of the file (an append). We can open with ‘a+’ to allow reading, seek backward and read (but all writes will still be at the end of the file.). Here’s a small demonstration:

apoorv@apoorv:~/Desktop$ python
Python 3.6.7 |Anaconda custom (64-bit)| (default, Oct 23 2018, 19:16:44)
[GCC 7.3.0] on linux
Type «help», «copyright», «credits» or «license» for more information.
>>> with open(‘testx.txt’, ‘w’) as f:
. f.write(‘This is a text for test purpose.’)
.
32
>>> with open(‘testx.txt’, ‘a’) as f:
. f.write(‘This is appended text!’)
.
22
>>> with open(‘testx.txt’, ‘r’) as f:
. f.read()
.
‘This is a text for test purpose.This is appended text!’
>>>

The numbers 32 and 22 returned by the functions are actually the number of characters in the content being written to the file.

Important: It should be noted that using ‘a’ is not the same as opening with ‘w’ and seeking to the end of the file! We should consider what might happen if another program opened the file and started writing between the seek and the write. Opening the file with ‘a’ guarantees that all of our following writes will be appended automatically to the end of the file even if the file grows by other writes.

Here’s one more demonstration about how the ‘a’ mode operates. Even if we seek back to the beginning, every write will append to the end of the file.

apoorv@apoorv:~/Desktop$ python
Python 3.6.7 |Anaconda custom (64-bit)| (default, Oct 23 2018, 19:16:44)
[GCC 7.3.0] on linux
Type «help», «copyright», «credits» or «license» for more information.
>>> f = open(‘demo1.txt’, ‘a+’)
>>> f.write(‘Hey’)
3
>>> f.seek(0)
0
>>> f.read()
‘Hey’
>>> f.write(‘ there.’)
7
>>> f.seek(0)
0
>>> f.read()
‘Hey there.’
>>>

Here’s a simple code about appending contents from one file to another. The second file name to be read is taken via command line:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('file_name', help='Provide the file name')
args = parser.parse_args()

fname = args.file_name

def main():
 
with open('app1.txt', 'r') as fread: 
print('\n**** Contents of file 1****') 
print(fread.read())
 
with open('app1.txt', 'a') as fappend: 
print(f'\nAppending the contents from from to currently ' + 
'opened file.') 
with open(fname, 'r') as fread: 
contents = fread.read() 
fappend.write(contents) 
print('Appended successfully!\n')
 
print('Now the contents of the app1.txt are : ') 
with open('app1.txt', 'r') as fread: 
print('\n**** Contents of file 1****') 
print(fread.read())


if __name__ == '__main__': 
main()

apoorv@apoorv:~/Desktop$ python append_file.py app2.txt

Appending the contents from from app2.txt to currently opened file.
Appended successfully!

Now the contents of the app1.txt are :

**** Contents of file 1****
These reflections have dispelled the agitation with which I began my
letter, and I feel my heart glow with an enthusiasm which elevates me
to heaven, for nothing contributes so much to tranquillize the mind as
a steady purpose—a point on which the soul may fix its intellectual
eye.
This is the most favourable period for travelling in Russia. They fly
quickly over the snow in their sledges; the motion is pleasant, and, in
my opinion, far more agreeable than that of an English stagecoach.

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How to Append Contents of One File to Another in Python

To append means to add on, usually to the end of something. You can also use append to mean to fix onto or to attach usually at the end. Sometimes you can change the meaning of a word by removing the suffix and appending another to it. This program takes the name of the file to be read from and the file to append into from the user and appends the contents of one file to another.and finally appends the content of one file to another file in this context.

STEP 1: Take the name of the file to be read from and the file to be appended into the user

STEP 2: Open the file to be read and read the content of the file and store it in a variable. The file to be read is opened using open() function in the read mode.

STEP 3: Open the file to append the data to and write the data stored in the variable into the file. The file to append the data is opened in the append mode and the data stored in the variable is written into the file.

STEP 4: Close both the files and exit from the program.

name1 = input("Enter file to be read from: ") name2 = input("Enter file to be appended to: ") file = open(name1, "r") data2 = file.read() file.close() fout = open(name2, "a") fout.write(data2) fout.close()

Enter file to be read from: test.txt Enter file to be appended to: test1.txt Contents of file test.txt: Appending!! Contents of file test1.txt (before appending): Original Contents of file test1.txt (after appending): Original Appending!!

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Python append to a file

While reading or writing to a file, access mode governs the type of operations possible in the opened file. It refers to how the file will be used once it’s opened. These modes also define the location of the File Handle in the file. The definition of these access modes is as follows:

Append Only (‘a’): Open the file for writing.
Append and Read (‘a+’): Open the file for reading and writing.

When the file is opened in append mode in Python, the handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.

Example 1: Python program to illustrate Append vs write mode.

Python3

Output of Readlines after appending This is Delhi This is Paris This is LondonToday Output of Readlines after writing Tomorrow

Example 2: Append data from a new line

In the above example of file handling, it can be seen that the data is not appended from the new line. This can be done by writing the newline ‘\n’ character to the file.

Python3

Output of Readlines after appending This is Delhi This is Paris This is London TodayTomorrow

Note: ‘\n’ is treated as a special character of two bytes.

Example 3: Using With statement in Python

with statement is used in exception handling to make the code cleaner and much more readable. It simplifies the management of common resources like file streams. Unlike the above implementations, there is no need to call file.close() when using with statement. The with statement itself ensures proper acquisition and release of resources.

Python3

Hello This is Delhi This is Paris This is London Today

Note: To know more about with statement click here.

Using the shutil module:

This approach uses the shutil.copyfileobj() method to append the contents of another file (source_file) to ‘file.txt’. This can be useful if you want to append the contents of one file to another without having to read the contents into memory first.

Approach:
The code uses the shutil.copyfileobj() function to copy the contents of the source_file object to a new file called file.txt. The with statement is used to open and automatically close the file, using the file object f.

Time Complexity:
The time complexity of shutil.copyfileobj() function is proportional to the size of the file being copied, as it needs to read and write every byte of the file. Therefore, the time complexity of the code is O(n), where n is the size of the source_file.

Space Complexity:
The space complexity of the code is O(1), as it does not allocate any additional memory beyond what is required for the file objects source_file and f. The shutil.copyfileobj() function copies the file contents in chunks, so it does not need to load the entire file into memory at once.

Overall, the code has a linear time complexity and constant space complexity, where the time complexity is proportional to the size of the file being copied.

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append one file to another

A very readable way to do this .

fin = open("File1.txt", "r") data1 = fin.read() fin.close() fin = open("File2.txt", "r") data2 = fin.read() fin.close() combined_data = data1 + data2 fout = open("File1&2.txt", "w") fout.write(combined_data) fout.close()

This can of course be simplified.

Or you can simply append …

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fin = open("File1.txt", "r") data1 = fin.read() fin.close() fin = open("File2.txt", "r") data2 = fin.read() fin.close() combined_data = data1 + data2 fout = open("File1&2.txt", "w") fout.write(combined_data) fout.close()

# append file2 data to file1 data fin = open("File2.txt", "r") data2 = fin.read() fin.close() fout = open("File1.txt", "a") fout.write(data2) fout.close()

hi can anybody tell me what does the following code mean?Thank you import sys
print >> sys.stderr, ‘Fatal error: invalid input!’ logfile = open(‘/tmp/mylog.txt’, ‘a’)
print >> logfile, ‘Fatal error: invalid input!’
logfile.close() Editor’s note:
Please don’t hijack someone else’s unrelated thread, start your own thread with the proper title.

[B]import[/B] sys [B]print [/B]>> sys.stderr, 'Fatal error: invalid input!' logfile = open('/tmp/mylog.txt', 'a') [B]print[/B] >> logfile, 'Fatal error: invalid input!' logfile.close()

We import the sys module documentation here
We print the message ‘Fatal error. etc’ to the system’s standard error pipe
Open a file located at /tmp/mylog.txt in ‘append’ mode, which means open it for writing but leave the existing contents intact (alternately could say ‘w’ for ‘write’ mode, which clears the contents when it opens the file)
Print the message into the logfile
Close the logfile.

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