13. Commonly used search methods
14.strip() function: remove the first and last information
15. Case conversion
16. About the formatting of strings
Center(), ljust(), rjust() these three functions are used to typeset strings
17. String formatting; padding and alignment
str.format() is used for string formatting, using {} and: instead of the previous%
padding and alignment are usually used together, ^,<,> are centered, left-aligned, and right-aligned respectively; with width at the back
: The filled character after the number can only be one character. If it is not specified, the default is a space
18. Number formatting
