Remove duplicate code by making `traceback.print_list()` delegate to `format_list()`

In Lib/traceback.py, the public helpers print_list() and format_list() independently contain the same formatting expression, so their outputs agree only by duplication. We propose routing print_list() through format_list() so that they share a single formatting path, with no change in behavior.

Problem

format_list() returns the formatted lines:

def format_list(extracted_list):
    return StackSummary.from_list(extracted_list).format()

print_list() writes those same lines, but re-derives them with the identical expression instead of reusing format_list():

def print_list(extracted_list, file=None):
    if file is None:
        file = sys.stderr
    for item in StackSummary.from_list(extracted_list).format():
        print(item, file=file, end="")

The outputs match only because StackSummary.from_list(extracted_list).format() is duplicated in both. Any future change to how a frame list is formatted has to be applied in both places to prevent the two public helpers from silently diverging.

Solution

Have print_list() iterate format_list():

def print_list(extracted_list, file=None):
    if file is None:
        file = sys.stderr
    for item in format_list(extracted_list):
        print(item, file=file, end="")

This eliminates the possibility of drift and mirrors the delegation already used in this module; for example, print_tb() calls print_list() rather than re-deriving extract_tb(...).format().

Linked PRs

• gh-153783

Bắt đầu trong Lib/traceback.py bằng cách so sánh các entry point print_list() và format_list() cùng các luồng định dạng hiện tại của chúng. Công việc được hoàn tất khi print_list() ủy quyền cho format_list() mà không thay đổi đầu ra hoặc việc xử lý tệp; issue có liên kết đến PR gh-153783, vì vậy hãy kiểm tra phần việc đó trước khi tiếp tục.