Using Python's str.format() for Advanced String Formatting

Python 2.6 introduced the str.format() function, which expands the capabilities of string formatting by replacing the older % operator with a more flexible syntax using {} and optional : specifiers.

Basic usage allows unlimited arguments and positional reordering, for example:

>>> "{} {}".format("hello", "world")  # 'hello world'
>>> "{0} {1}".format("hello", "world")  # 'hello world'
>>> "{1} {0} {1}".format("hello", "world")  # 'world hello world'

Named arguments can be supplied directly or via a dictionary:

print("网站名：{name}, 地址 {url}".format(name="测试天下", url="www.testtx.com"))
site = {"name": "测试天下", "url": "www.testtx.com"}
print("网站名：{name}, 地址 {url}".format(**site))

Lists can be referenced by index, and objects by attribute:

my_list = ["测试天下", "www.testtx.com"]
print("网站名：{0[0]}, 地址 {0[1]}".format(my_list))

class AssignValue(object):
    def __init__(self, value):
        self.value = value
my_value = AssignValue(6)
print('value 为: {0.value}'.format(my_value))

Numeric formatting supports precision, alignment, fill characters, sign handling, and type specifiers (binary, decimal, octal, hexadecimal). For example:

print("{:.2f}".format(3.1415926))  # 3.14

Alignment and fill are specified with ^ (center), < (left), > (right) followed by a width and an optional single‑character fill:

print("{:<10}".format("left"))   # left padded with spaces
print("{:*^10}".format("center")) # centered padded with '*'

Sign options + and a leading space can force display of positive signs or a leading space for positive numbers.

Braces can be escaped by doubling them:

print("{} 对应的位置是 {{0}}".format("testxt"))  # testxt对应的位置是{0}

A reusable template can be defined and formatted later, as shown:

tplt = "{:2}\t{:8}\t{:<16}"
print(tplt.format("序号", "价格", "商品名称"))

These examples demonstrate the versatility of str.format() for constructing dynamic strings in Python.