Best way to format integer as string with leading zeros?
PythonString FormattingPython Problem Overview
I need to add leading zeros to integer to make a string with defined quantity of digits ($cnt). What the best way to translate this simple function from PHP to Python:
function add_nulls($int, $cnt=2) {
$int = intval($int);
for($i=0; $i<($cnt-strlen($int)); $i++)
$nulls .= '0';
return $nulls.$int;
}
Is there a function that can do this?
Python Solutions
Solution 1 - Python
You can use the zfill() method to pad a string with zeros:
In [3]: str(1).zfill(2)
Out[3]: '01'
Solution 2 - Python
The standard way is to use format string modifiers. These format string methods are available in most programming languages (via the sprintf function in c for example) and are a handy tool to know about.
To output a string of length 5:
... in Python 3.5 and above: f-strings.
i = random.randint(0, 99999)
print(f'{i:05d}')
Search for f-strings here for more details.
... Python 2.6 and above:
print '{0:05d}'.format(i)
... before Python 2.6:
print "%05d" % i
Solution 3 - Python
Python 3.6 f-strings allows us to add leading zeros easily:
number = 5
print(f' now we have leading zeros in {number:02d}')
Have a look at this good post about this feature.
Solution 4 - Python
You most likely just need to format your integer:
'%0*d' % (fill, your_int)
For example,
>>> '%0*d' % (3, 4)
'004'
Solution 5 - Python
Python 2.6 allows this:
add_nulls = lambda number, zero_count : "{0:0{1}d}".format(number, zero_count)
>>>add_nulls(2,3)
'002'
Solution 6 - Python
For Python 3 and beyond: str.zfill() is still the most readable option
But it is a good idea to look into the new and powerful str.format(), what if you want to pad something that is not 0?
# if we want to pad 22 with zeros in front, to be 5 digits in length:
str_output = '{:0>5}'.format(22)
print(str_output)
# >>> 00022
# {:0>5} meaning: ":0" means: pad with 0, ">" means move 22 to right most, "5" means the total length is 5
# another example for comparision
str_output = '{:#<4}'.format(11)
print(str_output)
# >>> 11##
# to put it in a less hard-coded format:
int_inputArg = 22
int_desiredLength = 5
str_output = '{str_0:0>{str_1}}'.format(str_0=int_inputArg, str_1=int_desiredLength)
print(str_output)
# >>> 00022
Solution 7 - Python
You have at least two options:
- str.zfill:
lambda n, cnt=2: str(n).zfill(cnt) %formatting:lambda n, cnt=2: "%0*d" % (cnt, n)
If on Python >2.5, see a third option in clorz's answer.
Solution 8 - Python
One-liner alternative to the built-in zfill.
This function takes x and converts it to a string, and adds zeros in the beginning only and only if the length is too short:
def zfill_alternative(x,len=4): return ( (('0'*len)+str(x))[-l:] if len(str(x))<len else str(x) )
To sum it up - build-in: zfill is good enough, but if someone is curious on how to implement this by hand, here is one more example.
Solution 9 - Python
A straightforward conversion would be (again with a function):
def add_nulls2(int, cnt):
nulls = str(int)
for i in range(cnt - len(str(int))):
nulls = '0' + nulls
return nulls
Solution 10 - Python
This is my Python function:
def add_nulls(num, cnt=2):
cnt = cnt - len(str(num))
nulls = '0' * cnt
return '%s%s' % (nulls, num)