# Converting String to Complex Number in Python: Multiple Methods Explored

Converting String to Complex Number in Python: Multiple Methods Exploredπ‘ Problem Formulation:

In Python, a complex number is represented as `a + bj`, where `a` is the real part and `b` is the imaginary part. When we have a complex number in string format, such as `"3+4j"`, we may need to convert this back into a Python complex number object to perform arithmetic operations. This article demonstrates several methods to achieve this conversion, handling strings such as `"3+4j"` with the expected output being a complex number object: `3+4j`.

## Method 1: Using the complex() Constructor

The `complex()` constructor in Python can be used to turn a string into a complex number. It accepts strings formatted as `'real+imaginaryj'` and returns a complex number object. Note that spaces within the string are not allowed.

Here’s an example:

```num_str = "3+4j"
num_complex = complex(num_str)
print(num_complex)```

Output:

`(3+4j)`

This snippet demonstrates the direct conversion of a string representing a complex number into a complex number object using the built-in `complex()` function. The string `"3+4j"` is passed to the function, and it returns the complex number object `(3+4j)`.

## Method 2: Using ast.literal_eval

The `ast.literal_eval()` function can safely evaluate a string containing a Python literal or container display. It works well for strings that represent complex numbers and is a good choice when extra caution is needed to prevent code injection.

Here’s an example:

```import ast

num_str = "3+4j"
num_complex = ast.literal_eval(num_str)
print(num_complex)```

Output:

`(3+4j)`

This code utilizes the `ast.literal_eval()` method to evaluate the string `"3+4j"` as a literal expression, producing the complex number object `(3+4j)`. Itβs a safe alternative to the built-in `eval()` function.

## Method 3: Using Regular Expressions (re module)

By using regular expressions, we can parse the real and imaginary parts of a complex number from a string. This technique is useful if the string format can vary and may not be directly suitable for the `complex()` constructor.

Here’s an example:

```import re

num_str = "Real part: 3, Imaginary part: 4j"
match = re.search(r'([+-]?\\d+)([+-]?\\d+)?j', num_str)
num_complex = complex(match.group(1), match.group(2).rstrip('j'))
print(num_complex)```

Output:

`(3+4j)`

This snippet uses the Python `re` module to search for patterns in the string that represent the real and imaginary parts, then uses these parts to create a complex number object with the `complex()` constructor.

## Bonus One-Liner Method 4: Using eval with Safety Check

Warning: The `eval()` function should be used with caution, as it can execute arbitrary code. It’s included here for educational purposes and should be avoided or used very carefully.

Here’s an example:

```num_str = "3+4j"
num_complex = eval(num_str) if '+' in num_str or '-' in num_str else None
print(num_complex)```

Output:

`(3+4j)`

This one-liner uses a conditional expression to pass the string to `eval()` only if it contains `+` or `-`, to somewhat limit potential malicious content, though `eval()` still poses significant risks.

## Summary/Discussion

• Method 1: Using the complex() Constructor. This is the simplest and most straightforward method. It doesnβt require importing any modules. However, it only works if the string is properly formatted.
• Method 2: Using ast.literal_eval. Safe alternative to `eval()`. It works well but can be overkill for simple cases and is slower compared to the direct `complex()` constructor.
• Method 3: Using Regular Expressions. Very flexible and can handle various string formats. However, it adds complexity and requires careful handling of regular expression patterns.
• One-Liner Method 4: Using eval with Safety Check. Concise, but potentially very dangerous. It should be used with extreme caution and is not recommended for use in production code.