# Python File Handling (Reading and Writing)

File handling is an essential part of any application. Python has several functions for creating, reading, updating, and deleting files.

## Opening a File

The key function for working with files in Python is the `open()` function. The `open()` function takes two parameters: filename, and mode.

There are four different methods (modes) for opening a file:

*   `"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 exists.

In addition, you can specify if the file should be handled as binary or text mode:

*   `"t"` - Text - Default value. Text mode.
*   `"b"` - Binary - Binary mode (e.g. images).

## Reading Files

To open a file for reading, it is enough to specify the name of the file:

```python
f = open("demofile.txt", "r")
print(f.read())
```

### Read Only Parts of the File

By default the `read()` method returns the whole text, but you can also specify how many characters you want to return:

```python
f = open("demofile.txt", "r")
print(f.read(5))
```

### Read Lines

You can return one line by using the `readline()` method:

```python
f = open("demofile.txt", "r")
print(f.readline())
```

By looping through the lines of the file, you can read the whole file, line by line:

```python
f = open("demofile.txt", "r")
for x in f:
  print(x)
```

## Writing to an Existing File

To write to an existing file, you must add a parameter to the `open()` function:

*   `"a"` - Append - will append to the end of the file
*   `"w"` - Write - will overwrite any existing content

```python
f = open("demofile2.txt", "a")
f.write("Now the file has more content!")
f.close()
```

## The `with` Statement

It is good practice to use the `with` statement when working with files. This ensures that the file is closed properly, even if an exception is raised.

```python
with open("demofile.txt", "r") as f:
    content = f.read()
    print(content)
```

[[programming/python/python]]