一张图看懂Python3的字符串格式化

Python3里的字符串格式化功能很强大，新手看到下面的形式化描述可能会比较害怕：

format_spec     ::=  [[fill]align][sign][#][0][width][grouping_option][.precision][type]
fill            ::=  <any character>
align           ::=  "<" | ">" | "=" | "^"
sign            ::=  "+" | "-" | " "
width           ::=  digit+
grouping_option ::=  "_" | ","
precision       ::=  digit+
type            ::=  "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"

我先挑出比较常用的，画了一张图，每种用法都配了几个常用的例子：

当然，还有一张更全的。