How to return the position of numbers, which are same as input numbers, in a list in python?

问题

I have a list such as:

[1,2,3,2,1,5,6] 

I want to find the all the positions of 1 in the list. I tried if statement, but I only get the position of first 1, not all 1s.

The real output if I use if statement looks like [0], but the expected result should be [0,4].

回答1:

You can use a list comprehension iterating over enumerate(your_list) and using an if statement as part of it to catch only the wanted values, as below:

data = [1,2,3,2,1,5,6] # Your list
num = 1 # The value you want to find indices for

pos = [i for i, v in enumerate(data) if v == num]
print(pos)
# [0, 4]

回答2:

Try using enumerate:-> this give a tuple with its index and value from the list

 lndexs=[]
 for index,value in enumerate([1,2,3,2,1,5,6]):
        if value==1:
            lndexs.append( index)

回答3:

lstOfNumbers = [1,2,3,2,1,5,6]
searchFor = 1
lstOfIndexs = [index for index in range(len(lstOfNumbers)) if lstOfNumber[index]==searchFor]

Or you can use the python function filter

lstOfNumbers = [1,2,3,2,1,5,6]
searchFor = 1    
lstOfIndexs = filter(lambda x: lstOfNumbers[x]==searchFor, range(len(lstOfNumbers)))

来源：https://stackoverflow.com/questions/25804259/how-to-return-the-position-of-numbers-which-are-same-as-input-numbers-in-a-lis