Python String Formatting: Percent (%) and format() Methods with Detailed Examples

The article begins by introducing the percent (%) formatting style, showing the general syntax %[(name)][flags][width].[precision]typecode and describing each component such as name, flags (e.g., +, -, space, 0), width, precision, and typecode (s, r, c, d, o, x, X, e, E, f, F, g, G, %).

It then lists the meaning of each flag and typecode, explaining how to control alignment, sign display, padding, numeric bases, scientific notation, and percentage output. Sample percent‑format strings are provided, for example:

s1 = "i am %s, i am %d years old" % ('jeck', 26)

s2 = "i am %(name)s, i am %(age)d years old" % {'name':'jeck','age':26}

s3 = "i am %(name)+10s, i am %(age)d years old, i am %(height).2f" % {'name':'jeck','age':26,'height':1.7512}

s4 = "原数: %d, 八进制:%o , 十六进制:%x" % (15,15,15)

s5 = "原数:%d, 科学计数法e:%e, 科学计数法E:%E" % (1000000000,1000000000,1000000000)

s6 = "百分比显示:%.2f %%" % 0.75

Running the above snippets produces output such as:

i am jeck, i am 26 years old

i am     jeck, i am 26 years old, i am 1.75

原数:15, 八进制:17, 十六进制:f

原数:1000000000, 科学计数法e:1.000000e+09, 科学计数法E:1.000000E+09

百分比显示:0.75, 75.84%

The second part covers the newer format() method. It outlines the format string syntax {[fill][align][sign][#][0][width][,][.precision][type]} and explains each option, including fill characters, alignment (<, >, =), sign handling, alternate form (#), zero‑padding, width, thousands separator, precision, and type specifiers (s, d, b, o, x, X, e, E, f, F, g, G, %).

Example format() snippets are shown:

f1 = "i am {0}, i am {1}d years old".format('Jeck', 26)

f2 = "i am {name}, i am {age}d years old".format(**{'name':'jeck','age':26})

f3 = "--{name:*^10s}--   =={age:<10.2f}==".format(name='Jeck', age=26.457)

f4 = "原数:{:d}  二进制:{:b}, 八进制:{:o}, 十六进制x:{:x},十六进制X:{:X}".format(15,15,15,15,15)

f5 = "原数:{:d}, 科学计数法e:{:e}, 科学计数法E:{:E}".format(1000000000,1000000000,1000000000)

f6 = "原数:{:2F}, 百分号表示{:.2%},  原数:{:d},自动分割表示:{:,}".format(0.75,0.7584,10000000,10000000)

Printing these variables yields results such as:

i am Jeck, i am 26d years old

--***Jeck***--==26.46==

原数:15二进制:1111,八进制:17,十六进制x:f,十六进制X:F

原数:1000000000,科学计数法e:1.000000e+09,科学计数法E:1.000000E+09

原数:0.750000,百分号表示75.84%,原数:10000000,自动分割表示:10,000,000

Overall, the article serves as a concise reference for Python developers to master both legacy and modern string‑formatting techniques.