Search code examples
pythonstringlistformatdigits

add leading zeros to a list of numbers in Python


I am new to Python. I am trying to adjust the format of a list which looks like below:

data=[1,10,313,4000,51234,123456]

and I would like to convert them to a list of strings with leading zeros:

result=['000001','000010','000313','004000','051234','123456']

each of the element has 6 digits.

I know for a single number X, I can do:

str(X).zfill(6)

but I am not sure how to apply this to a list. I would like to solve this problem without using a for loop.

Anyone could help? Thanks.


Solution

  • Apply the same zfill function in a list comprehension, like this

    >>> [str(item).zfill(6) for item in data]
    ['000001', '000010', '000313', '004000', '051234', '123456']
    

    Alternatively, you can use the string's format method, with format specifiers, like this

    >>> ["{:06d}".format(item) for item in data]
    ['000001', '000010', '000313', '004000', '051234', '123456']
    

    If you are going to do the formatting more often, then you can store that in a variable, like this

    >>> formatter = "{:06d}".format
    >>> [formatter(item) for item in data]
    ['000001', '000010', '000313', '004000', '051234', '123456']
    

    If you are using Python 2.x, then you can use map and the formatter function, like this

    >>> map(formatter, data)
    ['000001', '000010', '000313', '004000', '051234', '123456']
    

    If you are using Python 3.x, map returns an iterable map object. So, you need to explicitly create a list, like this

    >>> list(map(formatter, data))
    ['000001', '000010', '000313', '004000', '051234', '123456']