------
## 最终结论
```python
def dig_let(s):
    letter_count = 0
    digit_count = 0
    for char in s:
        if char.isalpha():
            letter_count += 1
        elif char.isdigit():
            digit_count += 1
    return (letter_count, digit_count)

# Test cases
assert dig_let("python") == (6, 0)
assert dig_let("program") == (7, 0)
assert dig_let("python3.0") == (6, 2)
```