python - 如何在 str.format() 中使用宽度和精度变量？

Question

如何在 str.format() 规范中使用变量来表示宽度和精度？

(我使用的是 Python 3。)

这工作正常:

print('    {:<127.127}  {:<}'.format(value[1], value[0]))

但这会产生错误:

SHOWLEN = 127
print('    {:<SHOWLEN.SHOWLEN}  {:<}'.format(value[1], value[0]))

具体来说，我得到:

Traceback (most recent call last):

  File "C:\Users\Dave\Desktop\index\treeIndex.py", line 101, in <module>
    treeIndex(sys.argv[1])

  File "C:\Users\Dave\Desktop\index\treeIndex.py", line 96, in treeIndex
    print('    {:<SHOWLEN.SHOWLEN}  {:<}'.format(value[1], value[0]))

ValueError: Invalid format specifier

如何使用变量来表示精度和宽度？

Answer 1

将 SHOLEN 括在括号中

"{varname:<{SHOWLEN}.{SHOWLEN}f}".format(varname=34.54, SHOWLEN=8)

这从 Format String Syntax 的以下引用中可以明显看出文档:

A format_spec field can also include nested replacement fields within it. These nested replacement fields can contain only a field name; conversion flags and format specifications are not allowed. The replacement fields within the format_spec are substituted before the format_spec string is interpreted. This allows the formatting of a value to be dynamically specified.