Resolving the TypeError: How to Concatenate Strings and Lists in Python

Learn how to effectively concatenate strings in Python without encountering `TypeError`. This guide breaks down the solution to join wallet addresses using "|" as a separator.
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Resolving the TypeError: How to Concatenate Strings and Lists in Python

If you're a Python enthusiast, you might have encountered a frustrating TypeError that reads: "can only concatenate str (not 'list') to str." This error usually stems from an attempt to concatenate a string with a list, which simply isn't allowed in Python. In this guide, we will take a closer look at this common issue and how to resolve it, specifically in the context of building a URL for API requests.

Understanding the Error

Let’s break down the situation that leads to this error. The provided code snippet is meant to construct URLs for querying wallet balances using addresses retrieved from a CSV file. Here's the problematic line:

[[See Video to Reveal this Text or Code Snippet]]

Why the Error Occurs

In this line, you're trying to concatenate BASE_URL (a string) with a list containing a formatted string. Python does not allow concatenating lists directly to strings, which leads to the TypeError.

The Solution

To effectively concatenate the addresses and create a valid URL, you need to first convert the list of addresses into a single string, where each address is separated by a |. Let’s break it down into manageable steps.

Step 1: Join Wallet Addresses

You can use the join() method to create a single string from a list, using the desired separator:

[[See Video to Reveal this Text or Code Snippet]]

This line will create a string where all the wallet addresses are concatenated, separated by a pipe (|).

Step 2: Construct the URL

Once you have the address string, you can construct the URL more straightforwardly, as shown in the improved code snippet:

[[See Video to Reveal this Text or Code Snippet]]

Example Code

Here's how the complete make_api_url function might look after applying the changes:

[[See Video to Reveal this Text or Code Snippet]]

Summary

By understanding the error and utilizing the join() method, you can resolve the TypeError and effectively build your URLs for blockchain APIs. Remember:

Use join(): This minimizes string manipulation issues and simplifies your code.

Concatenate Strings Only: Always ensure you are concatenating compatible data types (i.e., strings with strings).

With these insights, you’ll have a better grasp of string manipulation in Python, paving the way toward smoother coding experiences!