status: #doc 
Tags: #python #programming 
links:[[python]] [[python/text]]
Date: 2023-04-30
___
# Read Text File in Python

## TL;DR
reading file and make list of lines of it
```python
with open('readme.txt') as f:
    lines = f.readlines()
```

## using open function

* first you must open a file with open function like this
```python
f = open("demofile.txt", "r")
```
OR
```python
with open('readme.txt', "r") as f:
```
open() return a file object that must go to file object in here we use `{f}` for storage , argument are
* first arg is file path 
* second arg is open mode

### open modes
open function have different modes (second arg)that can be seen [here](https://www.w3schools.com/python/ref_func_open.asp) but 4 most important are

- `"r"` - Read - Default value. Opens a file for reading, error if the file does not exist
- `"a"` - Append - Opens a file for appending, creates the file if it does not exist
- `"w"` - Write - Opens a file for writing, creates the file if it does not exist
- `"x"` - Create - Creates the specified file, returns an error if the file exist

### file object usage 

we can use file object with its [methods](https://www.w3schools.com/python/python_ref_file.asp) most common in use are 

- [`read()`](https://www.w3schools.com/python/ref_file_read.asp) - Returns all of the file content
- [`readline()`](https://www.w3schools.com/python/ref_file_readline.asp) - Returns one line from the file
- [`readlines()` ](https://www.w3schools.com/python/ref_file_readlines.asp)- Returns a list of lines from the file

usage example :
```python
f = open("demofile.txt", "r")  
print(f.read())
```
##  close() method

The file that you open will remain open until you close it using the `close()` method.

It’s important to close the file that is no longer in use for the following reasons:

-   First, when you open a file in your script, the file system usually locks it down so no other programs or scripts can use it until you close it.
-   Second, your file system has a limited number of file descriptors that you can create before it runs out of them. Although this number might be high, it’s possible to open a lot of files and deplete your file system resources.
-   Third, leaving many files open may lead to race conditions which occur when multiple [processes](https://www.pythontutorial.net/python-concurrency/differences-between-processes-and-threads/) attempt to modify one file at the same time and can cause all kinds of unexpected behaviors.

The following shows how to call the `close()` method to close the file:
```python
f.close()
```

To close the file automatically without calling the `close()` method, you use the `with` statement like this:

```python
with open(path_to_file) as f:
	contents = f.readlines()
```






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# References
https://www.pythontutorial.net/python-basics/python-read-text-file/