File splitting in python

What’s the fastest way to split a text file using Python?

Splitting a text file in Python can be done in various ways, depending on the size of the file and the desired output format. In this article, we will discuss the fastest way to split a text file using Python, taking into consideration both the performance and readability of the code.

split() method

One of the most straightforward ways to split a text file is by using the built-in split() function in Python. Based on a specified delimiter this function splits a string into a list of substrings.

For example, the following code splits a text file by newline characters and returns a list of lines −

with open('file.txt', 'r') as f: lines = f.read().split('\n')

• The built-in split() function splits a text file by newline characters and returns a list of lines.
• The code starts by opening the file using the open() function, with ‘r’ as the mode, which stands for reading. This returns a file object, which is stored in the variable f.
• Next, the read() method is used on the file object to read the entire contents of the file into memory as a single string.
• The split() function is then called on this string, with the newline character \n passed as the delimiter. This splits the string into a list of substrings, where each substring corresponds to a line in the original file. Finally, the result is stored in the variable lines.

readline() method

The previous method is simple and easy to read, but it can be slow for large files as it reads the entire file into memory before splitting it. If you are working with a large file, you may want to consider using the readline() method instead, which reads one line at a time.

with open('file.txt', 'r') as f: lines = [] for line in f: lines.append(line) 

• The code starts by opening the file in the same way as the previous example.
• Then we create an empty list called lines. Next, we use a for loop to iterate over the file object.
• The readline() method is called on the file object inside the for loop, which reads one line at a time from the file and assigns it to the variable line. This variable is then appended to the lines list.
• This way the entire file is read line by line and the lines are stored in the list.

This method is faster than the previous one as it reads one line at a time, and it does not require loading the entire file into memory. However, it still reads the entire file and can be slow for very large files.

mmap module

Another option is to use the mmap module in Python, which allows you to memory-map a file, giving you an efficient way to access the file as if it were in memory. Here’s an example of how to use mmap to split a text file −

import mmap with open('file.txt', 'r') as f: # memory-map the file mmapped_file = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) # split the file by newline characters lines = mmapped_file.read().split('\n') 

This method is the most efficient for large files, as it allows you to access the file as if it were in memory without actually loading the entire file into memory.

• The code starts by importing the mmap module.
• Next, the file is opened in the same way as before, and the fileno() method is called on the file object to get the file descriptor for the file.
• This is passed as the first argument to the mmap() function, along with 0 and mmap.ACCESS_READ as the second and third arguments, respectively. This memory maps the file, and the result is stored in the variable mmapped_file.
• The read() method is then called on the memory-mapped file, which reads the entire contents of the file into a single string, as before.
• The split() function is then called on this string, again with the newline character \n passed as the delimiter. This splits the string into a list of substrings, where each substring corresponds to a line in the original file. Finally, the result is stored in the variable lines.

Conclusion

In conclusion, the fastest way to split a text file using Python depends on the size of the file. If the file is small, the split() function or the readline() method can be used. However, for large files, the mmap module should be used to memory-map the file, providing a fast and efficient way to access the file.

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filesplit 4.0.1

Python module that is capable of splitting files and merging it back.

Навигация

Ссылки проекта

Статистика

Метаданные

Лицензия: MIT License

Метки file split, filesplit, split file, splitfile

Требует: Python >=3,

Сопровождающие

Классификаторы

Описание проекта

filesplit

File splitting and merging made easy for python programmers!

• Can split files of any size into multiple chunks and also merge them back.
• Can handle both structured and unstructured files.

System Requirements

Operating System: Windows/Linux/Mac

Python version: 3.x.x

Installation

The module is available as a part of PyPI and can be easily installed using pip

Split

 inputfile (str, Required) - Path to the original file.

outputdir (str, Required) — Output directory path to write the file splits.

With the instance created, the following methods can be used on the instance

bysize (size: int, newline: Optional[bool] = False, includeheader: Optional[bool] = False, callback: Optional[Callable] = None) -> None

size (int, Required): Max size in bytes that is allowed in each split.

newline (bool, Optional): Setting this to True will not produce any incomplete lines in each split. Defaults to False.

includeheader (bool, Optional): Setting this to True will include header in each split. The first line is treated as a header. Defaults to False.

callback (Callable, Optional): Callback function to invoke after each split. The callback function should accept two arguments [func (str, int)] — full path to the split file, split file size (bytes). Defaults to None.

bylinecount(self, linecount: int, includeheader: Optional[bool] = False, callback: Optional[Callable] = None) -> None

Splits file by line count.

linecount (int, Required): Max lines that is allowed in each split.

includeheader (bool, Optional): Setting this to True will include header in each split. The first line is treated as a header. Defaults to False.

callback (Callable, Optional): Callback function to invoke after each split. The callback function should accept two arguments [func (str, int)] — full path to the split file, split file size (bytes). Defaults to None.

The file splits are generated in this fashion [original_filename]_1.ext, [original_filename]_2.ext, . [original_filename]_n.ext .

A manifest file is also created in the output directory to keep track of the file splits. This manifest file is required for merge operation.

• The delimiter for the generated splits can be changed by setting splitdelimiter property like split.splitdelimiter=’$’ . Default is _ (underscore).
• The manifest file name for the generated splits can be changed by setting manfilename property like split.manfilename=’man’ . Default is manifest .
• To forcefully and safely terminate the process set the property terminate to True while the process is running.

Merge

 inputdir (str, Required) - Path to the directory containing file splits.

outputdir (str, Required) — Output directory path to write the merged file.

outputfilename (str, Required) — Name to use for the merged file.

With the instance created, the following method can be used on the instance

merge(cleanup: Optional[bool] = False, callback: Optional[Callable] = None) -> None

Merges the split files back into one single file.

cleanup (bool, Optional): If True, all the split files and manifest file will be purged after successful merge. Defaults to False.

callback (Callable, Optional): Callback function to invoke after merge. The callback function should accept two arguments [func (str, int)] — full path to the merged file, merged file size (bytes). Defaults to None.

• The manifest file name can be changed by setting manfilename property like merge.manfilename=’man’ . The manifest file name should match with the one used during the file split process and should be available in the same directory as that of file splits. Default is manifest .
• To forcefully and safely terminate the process set the property terminate to True while the process is running.

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How to Split File in Python

Python is a powerful programming language that allows you to easily work with files and data. Often you may need to split a file in Python, based on delimiter, size, lines, or column. In this article, we will learn how to split file in Python in different ways.

How to Split File in Python

Here are the different ways to split file in Python. Let us say you have a file data.txt that you want to split in Python.

Split File by Lines

In this case, we will split the contents of data.txt by lines. For example, let us say you have the following content in data.txt.

You can easily split a file in Python by lines using the built-in function splitlines(). Here is the code to do this.

f = open("data.txt", "r") content = f.read() content_list = content.splitlines() f.close() print(content_list)

Here is the output you will see when you run the above code. It will be a list, where each element is a line in your file data.txt

Let us look at the above code in detail. First, we open the file data.txt using open() function and store in a python object using read() function. We call splitlines() on this function, which returns a list, where each line in your file is a list item. Then we close the file using close() function and finally we print the contents our list using print() function.

Split File by Delimiter

In this case, we will split file based on a delimiter, also known as a separator. Typically, we get text files with tab delimited data and want to convert it into CSV file, or split it. For this purpose, we will use split() function, which allows you to split strings using separator. Let us say you have the following data.txt file with employee information.

Lana Anderson 585-3094-88 Electrician Elian Johnston 851-5845-87 Interior Designer Henry Johnston 877-6561-52 Astronomer

Here is a simple code to split the above file based on tab/space.

with open("data.txt",'r') as data_file: for line in data_file: data = line.split() print(data)

Here is the output you will see when you run the above code.

['Lana', 'Anderson', '485-3094-88', 'Electrician'] ['Elian', 'Johnston', '751-5845-87', 'Interior', 'Designer'] ['Henry', 'Johnston', '777-6561-52', 'Astronomer']

Let us look at the above code in detail. First, we open the file using open() function. Then we loop through the lines of the file using for loop. In each iteration, we call split() function on the line, which basically splits the string present in the line by ‘space’ separator. Finally, we print it using print() function.

Let us say you already have comma-separated strings on each line and want split() function to split each line using comma separator.

Janet,100,50,69 Thomas,99,76,100 Kate,102,78,65

Here is a simple code to use split() function to split such a file.

with open("data.txt",'r') as file: for line in file: data = line.strip().split(',') print(data)

Here is the output you will see.

['Janet', '100', '50', '69'] ['Thomas', '99', '76', '100'] ['Kate', '102', '78', '65']

In the above code, we open the file using open() function and run a for loop through its lines. In each iteration we call split() function and specify comma (,) as delimiter. This will split each line’s strings using comma separator. Finally, we call print() function to print its data.

Split File by Size

If you want to split a file by chunks or size then you need to use read() function to read fixed amount of file data and then work with it. Here is an example to do the same.

test_file = 'data.txt' def chunks(file_name, size=10000): with open(file_name) as f: while content := f.read(size): yield content if __name__ == '__main__': split_files = chunks(test_file) for chunk in split_files: print(len(chunk))

In the above code we define chunks() function that opens the file and reads specific amount of data from it and keeps returning the data as long as there is no more data to be read. We call this function and store the file chunks in split_lines list. We finally loop through split_lines list and print each chunk.

To be honest, is you are using Linux, it is advisable to simply use split command to split the file, based on size. Here is a command to easily do the above task in just 1 line.

In the above article, we have learnt how to split file in Python in various ways – by lines, delimiter and size. You can use any of the above code as per your requirement.

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