14.1 Reading from files

2 min read•june 24, 2024

Python's file input/output capabilities allow you to read from and write to files on your computer. This powerful feature enables you to work with external data, store program results, and manage persistent information across program executions.

The function is the gateway to file operations in Python. By understanding different file modes and reading methods, you can efficiently handle various file types and sizes, while proper closing practices ensure resource management and data integrity.

File Input/Output in Python

File opening with open()

Use the
```
open()
```
function to open a file and obtain a
- Syntax:
```
file_object = open(file_path, mode)
```
  - ```
  file_path
```
  represents the path to the file as a string (
```
  'data.txt'
```
  )
- ```
mode
```
    specifies how the file should be opened, default is ' for read mode (
```
'r'
```
    ,
```
'[rb'](https://www.fiveableKeyTerm:rb')
```
    )
Common read modes:
- 'r': read mode (default), opens the file for reading only, at the beginning
- 'rb': binary read mode, used for reading non-text files (images, audio)

Ensure the file exists and has read permissions to avoid

FileNotFoundError

[PermissionError](https://www.fiveableKeyTerm:PermissionError)

Consider the (absolute or relative) when opening files

Reading methods for file contents

```
[read()](https://www.fiveableKeyTerm:read())
```
reads the entire contents of a file as a single string
- Syntax:
```
file_contents = file_object.read()
```
- Returns an empty string when reaching the end of the file
```
[readline()](https://www.fiveableKeyTerm:readline())
```
reads a single line from the file
- Syntax:
```
line = file_object.readline()
```
- Returns an empty string at the end of the file
- Useful for reading large files line by line to avoid memory issues
```
[readlines()](https://www.fiveableKeyTerm:readlines())
```
reads all lines of a file and returns them as a list of strings
- Syntax:
```
lines = file_object.readlines()
```
- Each line becomes an element in the list (
```
['line1\n', 'line2\n']
```
  )
- Useful for processing file contents line by line
File pointer advances after each read operation, subsequent reads continue from the current position
Be aware of when reading lines from a file

Proper file closing practices

Always close files after reading or writing to free up system resources
- Syntax:
```
file_object.close()
```
Closing a file ensures:
- All data is written to the file (for write operations)
- File resources are released back to the operating system
- Other programs can access the file without conflicts

Use a

[try-finally](https://www.fiveableKeyTerm:try-finally)

block to ensure the file is always closed, even if an exception occurs

Syntax:

try:
    file_object = open(file_path, mode)
    # Perform file operations
finally:
    file_object.close()

Alternatively, use a

with

statement () to automatically close the file after the block

Syntax:

with open(file_path, mode) as file_object:
    # Perform file operations

Additional File Operations

: Use
```
file_object.seek()
```
to move the file pointer to a specific position
: Control how data is buffered when reading or writing files
: Specify the text encoding when opening files (e.g., UTF-8, ASCII)