Python string formatting with 'n' number of digits (when using keys) Python 2.7 [duplicate]

Question

To have specific number of digits in string formatting, I am aware that it can be done in this way:

In [18]: hours = 01

In [19]: "%.2d" %(hours)
Out[19]: '01'

In [20]: "%.2f" %(hours)
Out[20]: '1.00'

But my case is a bit different. I am using specific keys to denote the values, for example:

for filename in os.listdir('/home/user/zphot_01/')

Here I want to have different values for the '01', i.e.

for filename in os.listdir('/home/user/zphot_{value1}/'.format(value1=some_number):

When I use the above method with some_number = 01, it does not take into account the 0 and so my folder is not recognised.

EDIT:

Most of the answers are for only one value, however, I want to have more than one key value, i.e.:

for filename in os.listdir('/home/user/zphot_{value1}/zphot_{value2}'.format(value1=some_number1,value2=some_number2)).

Please use the new string formatting and you won't have a lot of these problems. — user1767754
– user1767754, Commented Nov 27, 2017 at 2:38
Or you could upgrade to Python 3.6 and use f-strings, Eg f'{value1:02}' — PM 2Ring
– PM 2Ring, Commented Nov 27, 2017 at 2:45

David Z · Accepted Answer · 2017-11-27 02:47:07Z

3

The new format string syntax allows you to use format specifiers, just like the old %-based syntax. The format specifiers you can use are similar, not exactly the same in all cases (I think), but as far as I know, anything you could do with the old syntax can also be done with the new syntax.

All you have to do is put the format specifier inside the formatting expression, separated from the field name/number by a colon. In this case, you could use {value1:02d}, where 02d is the code to get a zero-filled (0) width-2 (2) representation of an integer (d).

edited Nov 27, 2017 at 2:47

answered Nov 27, 2017 at 2:42

David Z

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8 Comments

Sraw Over a year ago

This is surely a more pythonic way than the other one.

Srivatsan Over a year ago

How to go about in Python 2.7 ?

David Z Over a year ago

The new string format codes also work in Python 2.7.

Srivatsan Over a year ago

@DavidZ: It doesn't! It still does not recognise the 0 in 01

David Z Over a year ago

@ThePredator What is that 0 supposed to mean? Are you talking about when you set hours = 01? You should know that in code, 1 and 01 represent exactly the same value

|

user1767754 · Accepted Answer · 2017-11-27 02:50:25Z

1

print("{0:02}".format(1))
>>0001

Just learnt from other answers and commentators that we don't need zfill but can use the expression :02 to give the padding.

Expand to more positions:

print("{0:02}_{1:02}".format(1, 2))
>>0001_0002

edited Nov 27, 2017 at 2:50

answered Nov 27, 2017 at 2:40

user1767754

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13 Comments

user1767754 Over a year ago

I love grumpy downvoters

user1767754 Over a year ago

I was about to iteratively make my answer better

PM 2Ring Over a year ago

There's no need for a separate .zfill call: .format can do that operation. Eg, "{0:02}".format(1)

cs95 Over a year ago

Um, your answer is now a carbon copy of DavidZ's...

cs95 Over a year ago

Still iterating, I'm not the downvoter.... but keep in mind that taking a solution someone else suggested first as yours is a little unfair to that other person.

|

Ender Look · Accepted Answer · 2017-11-27 03:03:17Z

1

There are a lot of ways. Look this answer.

This is my subjetive opinion, but I have ordered them by worst to best.

>>> '1'.zfill(2)
'01'
>>> '%02d' % 1
'01'
>>> '%02s' % '1'
'01'
>>> '{0:0>2}'.format(1)
'01'
>>> '{0:02d}'.format(1)
'01'
>>> '{:02d}'.format(1)
'01'
>>> f'{1:02}'
'01'

Then, you have to combine that with your current string, nothing really complicate.

Edit:

I am not sure what the OP is asking with his edit exactly but:

for filename in os.listdir('/home/user/zphot_{value1}/zphot_{value2}'.format(value1=some_number1,value2=some_number2)).

Can be changed by a lot of ways, I'll give some examples:

>>> number_first, number_second = '1', '2'
>>> '/home/user/zphot_{value1}/zphot_{value2}'.format(value1 = number_first.zfill(2), value2 = '2'.zfill(2))
'/home/user/zphot_01/zphot_02'
>>> '/home/user/zphot_{}/zphot_{}'.format('1'.zfill(2), number_second.zfill(2))
'/home/user/zphot_01/zphot_02'
>>> f'/home/user/zphot_{{number_first:02}}/zphot_{2:02}'
'/home/user/zphot_01/zphot_02'    
>>> '/home/user/zphot_%02d/zphot_%02s' % (1, '2')
'/home/user/zphot_01/zphot_02'
>>> '/home/user/zphot_{:02d}/zphot_{:02d}'.format(1, 2)
'/home/user/zphot_01/zphot_02'

Etc.

edited Nov 27, 2017 at 3:03

answered Nov 27, 2017 at 2:48

Ender Look

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5 Comments

Ender Look Over a year ago

@cᴏʟᴅsᴘᴇᴇᴅ, my english isn't really good and the translator think you are going to kill someone with "dupe target"... but, you're welcome, I guess.

Srivatsan Over a year ago

I want to use it for more than one value

Ender Look Over a year ago

@ThePredator, Could you explain better? I don't understand what are you meaning.

Srivatsan Over a year ago

I have edited my question, please look

Ender Look Over a year ago

@ThePredator, better?

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