Learning Contracts

What are Contracts

A Solidity contract is a piece of executable code consisting of state variables, functions, modifiers, and more. Contracts form the backbone of Solidity applications, defining the logic and rules that run on the the EVM.

Finding Contracts

Glider makes it easy to identify contracts using Glider’s Contracts class. Let’s see how this works by running the query below:

from glider import *

def query():
    return Contracts().exec(10)

After running the query, you should see the first 10 contract results found by Glider displayed in the Output panel.

Glider IDE contract output results

Foundational Contracts Query

Let's take a look at our foundational contracts query and break down the query code.

Query Goal

We are interested in finding "Market" contracts that are eligible to receive ERC-721 tokens. To find these contracts, we will search for contracts that have the name "Market" in them and contain the "onERC721Received" function.

The query is below:

from glider import *

def query():
    contracts = (
        Contracts()
        .with_name_regex("Market")
        .exec(1000)
        .filter(lambda contract : "onERC721Received" in contract.functions().exec().name)
    )

    return contracts

Now let's start by breaking down each query into sections below.

Step 1 - Finding Contracts

To find smart contracts, we first create an instance of the Contracts class:

Contracts()

Filtering Contracts by Name Using Regex

Next, we use the .with_name_regex() method provided by Glider. This method searches for contracts whose names match a given regular expression (regex).

Since we are looking for contracts that contain the term "Market", we pass "Market" as our regex pattern:

Contracts().with_name_regex("Market")

This ensures that any contract with "Market" in its name - such as "NFTMarket", "TokenMarketplace", or "MarketExchange" will be included in the results.

Step 2 - Filtering Contracts that Receive ERC-721 tokens

Now that we’ve queried for contracts with "Market" in their names, our next step is to ensure that our results only include contracts designed to receive ERC-721 tokens.

Contracts that expect to receive ERC-721 tokens must implement the onERC721Received function. If a contract does not define this function, it is not intending to receive ERC-721 tokens.

Filtering with .filter()

We add a .filter() method to our method call chain to exclude contracts that lack the onERC721Received function. The filter uses a lambda function to apply this criterion:

.filter(lambda contract: "onERC721Received" in contract.functions().exec().name)

Breaking Down the .filter() Function

Let’s take a closer look at how the .filter() function helps us refine our query results:

.filter(lambda contract : "onERC721Received" in contract.functions().exec().name)

Adding the Lambda Function

The .filter() method takes a lambda function, which is applied to every contract in the query results.

lambda contract : "onERC721Received" in contract.functions().exec().name

Retrieving All Functions in Each Contract

The lambda function first queries all functions in the contract:

contract.functions().exec()

Calling .functions() retrieves all defined functions in the contract and calling .exec() executes the query, returning a list of function objects.

Checking for onERC721Received

We then access the function names:

contract.functions().exec().name

This extracts the names of all functions defined in the contract.

Finally, calling "onERC721Received"in tells Glider to check if "onERC721Received" is inside the list of function names.

"onERC721Received" in contract.functions().exec().name

Tip: When we have a list of strings and want to check if a specific string exists in that list, we use the in keyword:

"term to look for" in list

If the function name exists in the list, the expression returns True. If the function does not exist, the expression returns False.

Filtering Out Results

Since .filter() only keeps results where the lambda function evaluates to True. This ensures that:

• Contracts defining onERC721Received remain in the results.

• Contracts without onERC721Received are filtered out.

This guarantees that our query only includes contracts capable of receiving ERC-721 tokens.

Step 3 - Returning Contracts

Once we’ve completed our query and filtered out unwanted results, we assign the final results to a variable named contracts and return it in the query() function:

return contracts

This ensures our results will be displayed in the Glider IDE Output panel.

Query Results

Running the Query

Now that we’ve covered the query, let’s run it in Glider IDE.

Paste the following query into the Glider IDE, click “Run”, and wait for the results:

from glider import *

def query():
    contracts = (
        Contracts()
        .with_name_regex("Market")
        .exec(1000)
        .filter(lambda contract : "onERC721Received" in contract.functions().exec().name)
    )

    return contracts

Interpreting the Results

Once the query completes, Glider returns a list of contracts and their addresses. Each contract in the results:

• Contains "Market" in its name, as specified in our query.

• Defines the onERC721Received function, confirming it is designed to receive ERC-721 tokens.

This ensures we have successfully filtered contracts that both match the "Market" naming criteria and are capable of handling ERC-721 token transfers.