如何在python中取数字的第n位数字
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How to take the nth digit of a number in python
提问by zakaria musa
I want to take the nth digit from an N digit number in python. For example:
我想从python中的N位数字中取出第n位数字。例如：
number = 9876543210
i = 4
number[i] # should return 6
How can I do something like that in python? Should I change it to string first and then change it to int for the calculation?
我怎么能在python中做这样的事情？我是否应该先将其更改为字符串，然后将其更改为 int 以进行计算？
采纳答案by Patrick Haugh
First treat the number like a string
首先将数字视为字符串
number = 9876543210
number = str(number)
Then to get the first digit:
然后得到第一个数字：
number[0]
The fourth digit:
第四位数字：
number[3]
EDIT:
编辑：
This will return the digit as a character, not as a number. To convert it back use:
这将返回数字作为字符，而不是数字。要将其转换回使用：
int(number[0])
回答by Chris Mueller
You can do it with integer division and remainder methods
您可以使用整数除法和余数方法来完成
def get_digit(number, n):
return number // 10**n % 10
get_digit(987654321, 0)
# 1
get_digit(987654321, 5)
# 6
The //performs integer division by a power of ten to move the digit to the ones position, then the %gets the remainder after division by 10. Note that the numbering in this scheme uses zero-indexing and starts from the right side of the number.
的//通过10的幂的整数除法进行的数字移动到的那些位置，则%通过10。注意得到余数，在本方案的编号使用从数的右侧的零索引和启动。
回答by Nathan Pyle
I would recommend adding a boolean check for the magnitude of the number. I'm converting a high milliseconds value to datetime. I have numbers from 2 to 200,000,200 so 0 is a valid output. The function as @Chris Mueller has it will return 0 even if number is smaller than 10**n.
我建议为数字的大小添加一个布尔检查。我正在将高毫秒值转换为日期时间。我有从 2 到 200,000,200 的数字，所以 0 是一个有效的输出。@Chris Mueller 所拥有的函数即使数字小于 10**n 也会返回 0。
def get_digit(number, n):
return number // 10**n % 10
get_digit(4231, 5)
# 0
def get_digit(number, n):
if number - 10**n < 0:
return False
return number // 10**n % 10
get_digit(4321, 5)
# False
You do have to be careful when checking the boolean state of this return value. To allow 0 as a valid return value, you cannot just use if get_digit:. You have to use if get_digit is False:to keep 0from behaving as a false value.
检查此返回值的布尔状态时，您必须小心。要允许 0 作为有效的返回值，您不能只使用if get_digit:. 您必须使用if get_digit is False:来0避免表现为错误值。
回答by Shayaan
I was curious about the relative speed of the two popular approaches - casting to string and using modular arithmetic - so I profiled them and was surprised to see how close they were in terms of performance.
我很好奇这两种流行方法的相对速度 - 转换为字符串和使用模块化算法 - 所以我对它们进行了分析，并惊讶地发现它们在性能方面有多接近。
(My use-case was slightly different, I wanted to get all digits in the number.)
（我的用例略有不同，我想获取数字中的所有数字。）
The string approach gave:
字符串方法给出：
10000002 function calls in 1.113 seconds
Ordered by: cumulative time
ncalls tottime percall cumtime percall filename:lineno(function)
10000000 1.113 0.000 1.113 0.000 sandbox.py:1(get_digits_str)
1 0.000 0.000 0.000 0.000 cProfile.py:133(__exit__)
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
While the modular arithmetic approach gave:
虽然模块化算术方法给出了：
10000002 function calls in 1.102 seconds
Ordered by: cumulative time
ncalls tottime percall cumtime percall filename:lineno(function)
10000000 1.102 0.000 1.102 0.000 sandbox.py:6(get_digits_mod)
1 0.000 0.000 0.000 0.000 cProfile.py:133(__exit__)
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
There were 10000000 tests run with a max number size less than 10000000000000000000000000000.
运行了 10000000 次测试，最大数量小于 10000000000000000000000000000。
Code used for reference:
参考代码：
def get_digits_str(num):
for n_str in str(num):
yield int(n_str)
def get_digits_mod(num, radix=10):
remaining = num
yield remaining % radix
while remaining := remaining // radix:
yield remaining % radix
if __name__ == '__main__':
import cProfile
import random
random_inputs = [random.randrange(0, 10000000000000000000000000000) for _ in range(10000000)]
with cProfile.Profile() as str_profiler:
for rand_num in random_inputs:
get_digits_str(rand_num)
str_profiler.print_stats(sort='cumtime')
with cProfile.Profile() as mod_profiler:
for rand_num in random_inputs:
get_digits_mod(rand_num)
mod_profiler.print_stats(sort='cumtime')
回答by GeekOverdose
Ok, first of all, use the str() function in python to turn 'number' into a string
好的，首先使用python中的str()函数将'number'转成字符串
number = 9876543210 #declaring and assigning
number = str(number) #converting
Then get the index, 0 = 1, 4 = 3 in index notation, use int() to turn it back into a number
然后得到索引，0 = 1, 4 = 3 用索引表示法，用 int() 把它变回数字
print(int(number[3])) #printing the int format of the string "number"'s index of 3 or '6'
if you like it in the short form
如果你喜欢它的简短形式
print(int(str(9876543210)[3])) #condensed code lol, also no more variable 'number'
