[Tut] How to Open Multiple Files in Python

[Tut] How to Open Multiple Files in Python - Printable Version

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[Tut] How to Open Multiple Files in Python - xSicKxBot - 06-11-2022

How to Open Multiple Files in Python

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In this article, you’ll learn how to open multiple files in Python.

Problem Formulation and Solution Overview

Question: How would we write Python code to open multiple files?

We can accomplish this task by one of the following options:

Method 1: Open Multiple Text Files using
Code:
open()
Method 2:Open Multiple Text Files using
Code:
open()
and backslash (
Code:
\
)
Method 3: Open Multiple Text Files using Parenthesized Context Managers and
Code:
open()
Method 4: Open Multiple Text Files using the os library and
Code:
open()

To make it more fun, we have the following running scenario:

You have been contacted by the Finxter Academy to write code that opens multiple files and writes the contents from one file to another.

Preparation & Overview

If your script opens files, it is a good practice to check for errors, such as:

No Such File Or Directory
Not Readable
Not Writable

In this regard, all examples in this article will be wrapped in a

Code:
try/except

statement to catch these errors.

Contents of

Code:
orig_file.txt

To follow along with this article, create

Code:
orig_file.txt

with the contents below and place it in the current working directory.

Code:
30022425,Oliver,Grandmaster,247630022437,Cindy,Intermediate,156930022450,Leon,Authority,1967

Add the following code to the top of each code snippet. This snippet will allow the code in this article to run error-free.

Code:
import logging

This allows us to log any error message that may occur when handling the files.

Method 1: Open Multiple Text Files with open()

This method opens multiple text files simultaneously on one line using the

Code:
open()

statement separated by the comma (

Code:
,

) character.

Code:
try: with open('orig_file.txt', 'r') as fp1, open('new_file.txt', 'w') as fp2: fp2.write(fp1.read())
except OSError as error: logging.error("This Error Occurred: %s", error)

This code snippet is wrapped in a

Code:
try/except

statement to catch errors. When this runs, it falls inside the

Code:
try

statement and executes as follows:

Opens two (2) text files on one line of code.
- The file for reading, which contains a comma (
  Code:
  ,
  ) character at the end to let Python know there is another file to open:
  Code:
  open('orig_file.txt', 'r') as fp1
- The second is for writing:
  Code:
  open('new_file.txt', 'w') as fp2
Then, the entire contents of
Code:
orig_file.txt
writes to
Code:
new_file.txt
.

If an error occurs during the above process, the code falls to the

Code:
except

statement, which retrieves and outputs the error message to the terminal.

Note: The

Code:
strip()

function removes any trailing space characters.
The newline character (

Code:
\n

) is added to place each iteration on its own line.

If successful, the contents of

Code:
orig_file.txt

and

Code:
new_file.txt

are identical.

Output of new_file.txt

Code:
30022425,Oliver,Grandmaster,247630022437,Cindy,Intermediate,156930022450,Leon,Authority,1967

Method 2: Open Files Across Multiple Lines with open() and Backslash (\)

Before Python version 3.10, and in use today, opening multiple files on one line could be awkward. To circumvent this, use the backslash (\) character as shown below to place the

Code:
open()

statements on separate lines.

Code:
try: with open('orig_file.txt', 'r') as fp1, \ open('new_file3.txt', 'w') as fp2: fp2.write(fp1.read())
except OSError as error: logging.error("This Error Occurred: %s", error)

This code snippet is wrapped in a

Code:
try/except

statement to catch errors. When this runs, it falls inside the

Code:
try

statement and executes as follows:

Opens the first file using
Code:
open('orig_file.txt', 'r')
for reading and contains a backslash (
Code:
\
) character to let Python know there is another file to open.
Opens the second file using
Code:
open('new_file.txt', 'w')
for writing.
Then, the entire contents of
Code:
orig_file.txt
writes to
Code:
new_file.txt
.

If an error occurs during the above process, the code falls to the

Code:
except

statement, which retrieves and outputs the error message to the terminal.

Note: The

Code:
strip()

function removes any trailing space characters.
The newline character (

Code:
\n

) is added to place each iteration on its own line.

If successful, the contents of

Code:
orig_file.txt

and

Code:
new_file.txt

are identical.

Method 3: Open Multiple Text Files using Parenthesized Context Managers and open()

In Python version 3.10, Parenthesized Context Managers were added. This fixes a bug found in version 3.9, which did not support the use of parentheses across multiple lines of code. How Pythonic!

Here’s how they look in a short example:

Code:
try: with ( open('orig_file.txt', 'r') as fp1, open('new_file.txt', 'w') as fp2 ): fp2.write(fp1.read())
except OSError as error: logging.error("This Error Occurred: %s", error)

This code snippet is wrapped in a

Code:
try/except

statement to catch errors. When this runs, it falls inside the

Code:
try

statement and executes as follows:

Declare the opening of
Code:
with
and the opening bracket (
Code:
with (
)).
- Opens
  Code:
  orig_file.txt
  (
  Code:
  open('orig_file.txt', 'r') as fp1,
  ) for reading with a comma (,) to let Python know to expect another file.
- Open
  Code:
  new_file.txt
  (
  Code:
  open('new_file.txt', 'w') as fp2
  ) for writing.
Closes the
Code:
with
statement by using
Code:
):
.
Then, the entire contents of
Code:
orig_file.txt
writes to
Code:
new_file.txt
.

If an error occurs during the above process, the code falls to the

Code:
except

statement, which retrieves and outputs the error message to the terminal.

If successful, the contents of

Code:
orig_file.txt

and

Code:
new_file.txt

are identical.

Method 4: Open Multiple Text Files using the os library and open()

This method calls in the

Code:
os

library (

Code:
import os

) which provides functionality to work with the Operating System. Specifically, for this example, file and folder manipulation.

Code:
import os os.chdir('files')
filelist = os.listdir(os.getcwd()) for i in filelist: try: with open(i, 'r') as f: for line in f.readlines(): print(line) except OSError as error: print('error %s', error)

Note: In this example, two (2) files are read in and output to the terminal.

This code snippet imports the

Code:
os

library to access the required functions.

For this example, we have two (2) text files located in our

Code:
files

directory:

Code:
file1.txt

and

Code:
file2.txt.

To access and work with these files, we call

Code:
os.chdir('files')

to change to this folder (directory).

Next, we retrieve a list of all files residing in the current working directory
(

Code:
os.listdir(os.getcwd()

) and save the results to

Code:
filelist

.

IF we output the contents of

Code:
filelist

to the terminal, we would have the following: a list of all files in the current working directory in a List format.

Code:
['file1.txt', 'file2.txt']

This code snippet is wrapped in a

Code:
try/except

statement to catch errors. When this runs, it falls inside the

Code:
try

statement and executes as follows:

Instantiates a
Code:
for
loop to traverse through each file in the List and does the following:
- Opens the current file for reading.
- Reads in this file one line at a time and output to the terminal.

If an error occurs during the above process, the code falls to the

Code:
except

statement, which retrieves and outputs the error message to the terminal.

Output

The contents of the two (2) files are:

Code:
Contents of File1.Contents of File2.

Summary

These four (4) methods of how to multiple files should give you enough information to select the best one for your coding requirements.

Good Luck & Happy Coding!

Programmer Humor

Code:
Question: How did the programmer die in the shower? ☠

❗ Answer: They read the shampoo bottle instructions:
Lather. Rinse. Repeat.