Formatting lists of objects in python

Question

I have read a lot of similar questions related to my question, but I have not seen any specifically for this. I have a list of objects, such as

l = ((a, 0.5), (b, 0.75), (c, 0.954367))

I want to be able to print out only the numbers, formatted to 5 decimal places. I was not too sure how to go about this, so I started by trying to slice it and then print it as such

nums = list(z[1:2] for z in l)    # originally had 'tuple' instead of 'list'
print("numbers: {:.5f}".format(nums))

The slicing works, giving me only the numbers, but when I get to the print statement I get an error

TypeError: non-empty format string passed to object.__format__

I originally had the slicing to be done as a tuple, but thought that that may have been causing the error so changed it to a list, which did not help. One answer I read noted that "bytes objects do not have a _ _format__ method of their own, so the default from object is used." and suggested converting it to a string instead - which resulted in the same error.

My question essentially, is there a way to fix this error, or a better way to get the output without slicing/using the method above?

Thank you,

Ahasanul Haque · Accepted Answer · 2017-04-11 16:58:52Z

1

Use simple list comprehension.

>>> l = (('a', 0.5), ('b', 0.75), ('c', 0.954367))
>>> ["{:.5f}".format(i[1]) for i in l]
[ '0.50000', '0.75000', '0.95437']

answered Apr 11, 2017 at 16:58

Ahasanul Haque

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Dimitris Fasarakis Hilliard · Accepted Answer · 2017-04-11 16:59:11Z

1

You're trying to use a float presentation type, 'f', with a list object. That's the cause of the failure.

Supply print with a list comprehension of the formatted values which you can unpack and provide as positionals:

print("numbers: ", *["{0[0]:.5f}".format(i) for i in nums])

This now prints out:

numbers:  0.50000 0.75000 0.95437

answered Apr 11, 2017 at 16:59

Dimitris Fasarakis Hilliard

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Comments

John Moutafis · Accepted Answer · 2017-04-11 22:27:03Z

-1

try:

nums = list(z[1] for z in l)

z[1:2] essentially gives another list of numbers: [[0.5],[0.75],[0.954367]], which I don't think you require.

edited Apr 11, 2017 at 22:27

John Moutafis

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answered Apr 11, 2017 at 16:59

AMIT KUMAR SHARMA

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2 Comments

vincentmajor Over a year ago

This answer does not address the 5 decimal place formatting constraint.

AMIT KUMAR SHARMA Over a year ago

this answer was for first line , second line in question was already taking care of 5 decimal point

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