String Representation of List: How to Convert it Back into a List?
Numerous programming languages enable us to convert a list into a string representation, effectively storing a list’s contents in a single string variable.
This string variable can then be easily stored in a file or transmitted over a network. However, the challenge arises when we need to convert this string back into its original list form.
Thankfully, there are multiple ways to do it, and this article will introduce you to some of the most common ones.
1. ast.literal_eval()
First on the list is the safest method, i.e., using ast.literal_eval(). This method is considered the best option to convert a string variable that contains a Python list to a list.
The ast.literal_eval() function is a part of python’s built-in ‘ast’ module, which allows you to safely evaluate expressions containing Python literals. Here is an example:
import ast
str_list = "[1, 2, 3, 4, 5]"
list_ = ast.literal_eval(str_list)
print(list_)
Output:
[1, 2, 3, 4, 5]2. strip()
The str.strip() function eliminates whitespaces from the beginning and end of a string.
We can use this function to initialize a string without brackets, creating a string representation of a list’s content, separated by commas. Here is an example:
str_list = "[1, 2, 3, 4, 5]"
str_list = str_list.strip('[]')
list_ = str_list.split(',')
print(list_)
Output:
['1', ' 2', ' 3', ' 4', ' 5']Note: This method produces a list of string objects. If you want integers, you can use a built-in function ‘int’.
3. JSON string to Python list
An alternative method to handle string representation of lists is to serialize and de-serialize JSON (JavaScript Object Notation) strings.
The JSON module in Python offers functions to serialize Python objects into JSON formatted strings and deserialize the JSON formatted strings into Python objects. Here is an example:
import json
str_list = "[1, 2, 3, 4, 5]"
list_ = json.loads(str_list)
print(list_)
Output:
[1, 2, 3, 4, 5]This method is considered relatively safe, as long as you restrict your JSON input to a set of types that JSON de-serializes safely.
4. re.findall()
We can also use regular expressions to convert a string representation of a list into a Python list. Here is an example:
import re
str_list = "[1, 2, 3, 4, 5]"
list_ = re.findall(r'd+', str_list)
print(list_)
Output:
['1', '2', '3', '4', '5']This method uses a regular expression pattern to extract all substrings containing numeric digits.
5. eval()
One of the most widely used methods for converting a string representation of a list to a Python list is to use the built-in eval() function. The eval() function evaluates a Python expression that is in string form.
However, the use of eval() function is considered especially unsafe when evaluating user input, as it can execute malicious code. Using eval() is discouraged, and it is suggested to use ast.literal_eval() instead.
Here is an example:
str_list = "[1, 2, 3, 4, 5]"
list_ = eval(str_list)
print(list_)
Output:
[1, 2, 3, 4, 5]6. map()
Another popular method is to use Python’s built-in map() function and convert each string element to an integer.
Here is an example:
str_list = "[1, 2, 3, 4, 5]"
list_ = list(map(int, str_list.strip('[]').split(',')))
print(list_)
Output:
[1, 2, 3, 4, 5]This method applies the int() class to each string element in a list.
7. PyYAML module
The PyYAML module in Python can also parse YAML configurations safely. Here is an example:
import yaml
str_list = "[1, 2, 3, 4, 5]"
list_ = yaml.safe_load(str_list)
print(list_)
Output:
[1, 2, 3, 4, 5]However, it is essential to ensure you are parsing trusted input data to minimize security risks. PyYAML also provides a yaml_full_load() function that might be useful but should be used with caution.
In conclusion, there are numerous ways to convert string representations of lists back into a list in Python. Each method has its pros and cons, and some of them are better suited for specific situations than others.
It is crucial to choose a method that is both safe and appropriate for your use case. In summary, this article delved into various methods that can be used to convert string representation of a Python list back into a list.
While some methods like ast.literal_eval() and JSON to Python list are safer than others, it is essential to choose a method appropriate for your use case. In conclusion, the ability to quickly convert string representations into a Python list is a crucial skill for any Python developer, and the methods outlined here provide a starting point for this process.
Remember to prioritize safety when choosing a method, and always think carefully about the data you are working with.