How do I pad a string with zeroes?

More padding, more options

Sure, zfill() is quick and sweet. But Python isn't a one-trick snake! Let me introduce some alternate padding options:

Padding with f-strings (Python 3.6+)

The f-string can also pad your lonely string:

n = 42
# 42 special characters in ASCII... Coincidence? I think not!
f"{n:05}"  # '00042'
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This method is both concise and readable, and even allows for in-string expressions. Yes, you heard that right!

Padding with .format and %

Ever heard of the .format() method? It's a bit old school, but it still does the trick:

# It's good to put names to faces. Or numbers...
"{number:05d}".format(number=42)  # '00042'
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Or with % formatting (even older, but still gold):

# % is basically the history teacher of Python.
"%05d" % 42  # '00042'
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.format() is flexible like a good yoga teacher, % is like your grandma: familiar, comforting, but a bit old-fashioned.

Padding with rjust and ljust

What if your string doesn't identify as a number? No problemo! Meet rjust and ljust:

# A "test" that passes before it begins!
"test".rjust(8, '0')  # '0000test'
"test".ljust(8, '0')  # 'test0000'
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These methods are for those who want extra control on alignment, or for those little rebels who want to pad to the right!

Padding: Redux

Named placeholders

Need to make your padding intentions clear? Look no further than named placeholders:

# Names, the key to destiny.
"{filename:020}".format(filename="report")  # '00000000000000report'
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Express inline formatting

Sometimes, you need to pad right in the middle of the action:

# The day the date stood still.
f"Date: {year:04}-{month:02}-{day:02}"  # 'Date: 2023-03-14'
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Left or right? It's your right!

Choose your padding side according to your needs:

# Left or Right? Only the oracle knows.
left_padded = "42".rjust(5, '0')  # '00042'
right_padded = "42".ljust(5, '0')  # '42000'
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Visual impact and data parsing might tip the scale!

Variable length? Loop it!

Got a variable-length list? Just use a loop:

# The circle of life, for numbers.
numbers = [5, 50, 500]
padded = [f"{n:03}" for n in numbers]  # ['005', '050', '500']
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This way, uniformity is enforced on dynamic data, making everything zen.

Digging deeper

Organised chaos

Zero-padding helps maintain numerical order even in a string datatype:

# Who ordered a string of numbers?
"2".zfill(3)  # '002'
"10".zfill(3)  # '010'
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Wait, are you a number or a string?

Do check and convert non-string types before padding:

# Just making sure...
str(42).zfill(5)  # '00042'
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Python won't be mad with wrong padding width, but might give you a funny look:

# Maybe you counted on your fingers?
"42".zfill(2)  # '42'
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Mixin' it up

Get fancy with mixed formatters for eclectic padding parties:

# Time for a formatted party!
f"{hour:02}:{minute:02}:{second:02}"  # 'Hours:Minutes:Seconds with padding'
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Consistency in padding enhances both data readability and your karma.