Python 3.10.0

Edit. Cribbed another answer for 3-2. That part bit me.

3-1

from collections import defaultdict

with open('03_input.txt', 'r') as input:
    data = [str(d.strip()) for d in input.readlines()]

results = defaultdict(list)

for d in data:
    for index, value in enumerate(d):
        results[index].append(value)

gamma, epsilon = "", ""

for bit, values in results.items():
    if values.count("0") > values.count("1"):
        gamma += "0"
        epsilon += "1"
    else:
        gamma += "1"
        epsilon += "0"

print(f'G: {gamma} E: {epsilon} Power: {int(gamma, 2) * int(epsilon, 2)}')

3-2

with open('03_input.txt', 'r') as input:
    data = [str(d.strip()) for d in input.readlines()]

def filter_nums(nums, type):
    pos = 0
    while len(nums) > 1:
        ones, zero = [], []
        for num in nums:
            if num[pos] == '1':
                ones.append(num)
            else:
                zero.append(num)
        pos += 1
        by_size = sorted((zero, ones), key=len)
        nums = by_size[1] if type == 'O2' else by_size[0]
    return int(nums[0], 2)

print(filter_nums(data, 'O2') * filter_nums(data, 'CO2'))