Quiz of the day: print format

[TrustyTony]

What does this print statement produce and why? Learned it today, I still must be a newbie.

print('%0*d' % (3, 7))

[m4ster_r0shi]

Ok, since  nobody  has  replied  yet, I  thought  I'd  give  it a shot.
Warning -> I'm not an expert, at all. I just started learning python.

The above  statement   prints 7, left zero  padded,  so that  the total
number of digits is 3. You can also put 3 in the format string instead:

print('%03d' % 7)

[M.S.]

Is "d" here stands for "digit"?
this bellow code does the same but instead of 0's it prints empty spaces"

print('%0*s' % (3, 7))

what about "s" here? does it mean "string"?

[Gribouillis]

Is "d" here stands for "digit"?
this bellow code does the same but instead of 0's it prints empty spaces"

print('%0*s' % (3, 7))

what about "s" here? does it mean "string"?

Yes, 's' means string. In principle, the str() method is applied to the argument. Better learn to use the new format() operator which is more powerful than %. For example

>>> print( "{0:{1}^{2}s}".format(" 77 ", "=", 60) )
============================ 77 ============================

Some more examples here http://www.daniweb.com/software-development/python/code/232375

[TrustyTony]

It is more like 'use the objects __str__ method ie use str function to object'

How about these, then:

print('%*r' % (6, '7'))
 print('%*r' % (6, 7))

Yes, format is good to learn also, but there is lot of code with 'modulo formatting', so you better learn both.

[TrustyTony]

Yes, 's' means string. In principle, the str() method is applied to the argument. Better learn to use the new format() operator which is more powerful than %. For example

>>> print( "{0:{1}^{2}s}".format(" 77 ", "=", 60) )
============================ 77 ============================

Some more examples here http://www.daniweb.com/software-development/python/code/232375

Shows that the language of format is powerfull, but I would still prefer for readability:

print(' 77 '.center(60, '='))

or

print( "{info:{char}^{width}s}".format(info=" 77 ", char="=", width=60))

[TrustyTony]

What this new format function does and how it works?

def print_formats(num):
    print('{num:016b} {num:04x} {num:06o} {num:05d}'.format(**locals()))

print_formats(1234)

[TrustyTony]

It is more like 'use the objects __str__ method ie use str function to object'

How about these, then:

print('%*r' % (6, '7'))
 print('%*r' % (6, 7))

Yes, format is good to learn also, but there is lot of code with 'modulo formatting', so you better learn both.

>> print('%*r' % (6, '7'))
   '7'
>>> print('%*r' % (6, 7))
     7

So for repr the quotes count for width, so string 7 start two spaces before than number 7 to finish at same position.

And how about this then, what it does?

print('%u' % -7)

[M.S.]

I think It only accepts Integers and convert them to Unicode strings:

>>> a='%u' % -7
>>> print type(a)
<type 'str'>

[TrustyTony]

I think It only accepts Integers and convert them to Unicode strings:

>>> a='%u' % -7
>>> print type(a)
<type 'str'>

Nope it is not, and it is not (anymore) unsigned integer like in C, but it is synonym for %i and %d. Better to avoid using it, as it will be deprecated and is only confusing. This is only to show "Python is not C".

[vegaseat]

Python27 and higher ...

# pad with leading zeroes
print( "value is {v:0{digits}n}".format(v=2, digits=3) )

"""result -->
value is 002
"""

[Purkinje]

I know this thread is more than 2 weeks old, but I have a question about the format() syntax.

print( "{0:{1}^{2}s}".format(" 77 ", "=", 60) )

When specifying the field_name, you don't need to place {} around the '0'. I understand that it refers to the 0th element of the list. However, the fill character field is specified here by {1}, and the width field is specified by {2}. These obviously also refer to the list passed in format(), but they include {}.

I can't find anything in the documentation to indicate why this is. Could someone explain why this syntax is used?

[TrustyTony]

Those two are nested inside a format specifier not information to print.

>>> print( ":{0}^{1}s".format("=", 60) )
:=^60s
>>> print( "{0:=^60s}".format(" 77 ") )
============================ 77 ============================
>>>

[Purkinje]

Those two are nested inside a format specifier not information to print.

That wasn't my question. I was simply questioning the syntax of the format specifier, which I could not find in the documentation. Outside of the format specifier, Python, in general, uses '{' and '}' to refer to dictionary declarations. However, within the format specifier, it refers to elements within the tuple passed into the format() method. Why use {} within the format_spec, but not the field_name?

Please see http://docs.python.org/library/string.html#format-string-syntax for the meaning of the bolded terms I used.

[TrustyTony]

It is dictionary in general sense, but you can access unspecified keys by numeric key:

>>> family
{'father': 'Tony', 'mother': 'Edlira'}
>>> print("Father is {father} and mother is {mother}".format(**family))
Father is Tony and mother is Edlira

[Purkinje]

Ah, thanks for the clarification on that. I appreciate your help! It's interesting to see what you can do with strings.