Python 当字符串中有 ANSI 转义序列字符时忽略字符串格式

Question

Why does string formatting get ignored when ANSI escape sequence characters are included in the string?

Example (Python 3.9.1) :

execution_times = [0, 12]
for execution_time in execution_times:
    affected_row_count = 26953
    c = ''
    cgrey = ''
    endc = ''
    
    if execution_time == 0:
        cgrey = '\33[90m'
    
    if execution_time > 0:
        c = '\033[94m'
        endc = '\033[0m'
    
    rows_affected_text = f' ({affected_row_count} rows affected)'
    elapsed_time_text = f'Elapsed Time: {c}{execution_time}{endc} secs'
    
    print(f'{cgrey}{elapsed_time_text:25s}{rows_affected_text}\033[0m')

Expected output would be:

Elapsed Time: 0 secs      (26953 rows affected)
Elapsed Time: 12 secs     (26953 rows affected)

but instead it yields

Elapsed Time: 0 secs      (26953 rows affected)
Elapsed Time: 12 secs (26953 rows affected)

The :25s string formatting is being ignored; what am I missing?

Answer 1

Because cgrey , c and endc are taken into account when calculating the alignment format.

Try to print raw bytes of the string.

# ...
    x = f'{cgrey}{elapsed_time_text:25s}{rows_affected_text}\033[0m'
    print(x)
    print(x.encode())

Result:

Elapsed Time: 0 secs      (26953 rows affected)
b'\x1b[90mElapsed Time: 0 secs      (26953 rows affected)\x1b[0m'
Elapsed Time: 12 secs (26953 rows affected)
b'Elapsed Time: \x1b[94m12\x1b[0m secs (26953 rows affected)\x1b[0m'