在此任务中，你需要编写一个函数，将所有字符串元素的所有字符转换为大写字母，并返回一个新的列表。如果输入不是列表，则应该输出一个错误消息。
def upper_case_list(input_list):
"""Convert all string elements in input_list to uppercase"""
# TODO: Implement function
input_list = ['hello', 'world', 'python']
Here is an implementation of the function:

```
def upper_case_list(input_list):
    if not isinstance(input_list, list):
        return "Error: input is not a list"
    new_list = []
    for item in input_list:
        if isinstance(item, str):
            new_list.append(item.upper())
        else:
            new_list.append(item)
    return new_list
```

This function first checks if the input is a list or not. If it's not a list, it returns an error message.

Next, it creates an empty list to hold the converted strings. It loops through each element of the input_list and checks if it's a string or not. If it's a string, it converts it to uppercase using the `upper()` method and appends it to the new_list. If it's not a string, it appends it to the new_list as it is.

Finally, it returns the new_list containing all the uppercase strings. 

When the function is called with the input list `['hello', 'world', 'python']`, the output would be `['HELLO', 'WORLD', 'PYTHON']`.