## For Loops In this lesson we will explore the `for` loop in Vyper. We will first use a for loop to iterate over a range of integers. We can use the `range` function to specify the starting and ending index of the loop. ```python @external @pure def for_loop() -> DynArray[uint256]: arr: DynArray[uint256, 10] = [] for i: uint256 in range(5): arr.append(i) return arr ``` In the above code, we are using a for loop to iterate over the first 5 integers. For each iteration, we append the current integer to the `arr`. Finally, we return the `arr`. We can also iterate over a fixed-size list. ```python @external @pure def for_loop_list() -> DynArray[uint256]: arr: DynArray[uint256, 10] = [] nums: uint256[4] = [11, 22, 33, 44] for i: uint256 in nums: arr.append(i) return arr ``` In this code, we are iterating over the fixed-size list `nums` and appending each element to the `arr`. You can also skip iterations using the `continue` keyword. For example: ```python @external @pure def for_loop_skip() -> DynArray[uint256]: arr: DynArray[uint256, 10] = [] nums: uint256[4] = [11, 22, 33, 44] for i: uint256 in nums: if i == 2: continue arr.append(i) return arr ``` In the code above, we are iterating over the list `nums`. If the current element is equal to 2, the `continue` keyword will skip the rest of the code for that iteration and move on to the next iteration. You can also break out of a for loop early using the `break` keyword. ```python @external @pure def for_loop_break() -> DynArray[uint256]: arr: DynArray[uint256, 10] = [] nums: uint256[4] = [11, 22, 33, 44] for i: uint256 in nums: if i == 2: continue if i == 4: break arr.append(i) return arr ``` In this code, we are iterating over the list `nums`. If the current element is equal to 2, the `continue` keyword will skip the rest of the code for that iteration and move on to the next iteration. If the current element is equal to 4, the `break` keyword will exit the for loop. To reset the elements of a hashmap to zero, we can use a for loop. ```python for funder: address in self.funders: self.funder_to_amount_funded[funder] = 0 ``` The code above iterates through each address in the `self.funders` list and sets the corresponding value in the `self.funder_to_amount_funded` hashmap to 0. We can also iterate through the `self.funders` list using a for each loop. ```python for funder: address in self.funders: self.funder_to_amount_funded[funder] = 0 ``` Using a for loop to reset the values in a hashmap will use a lot of gas. You should carefully consider the gas costs and trade-offs of different data structures when designing your smart contracts.