No int variables allowed in Python string replacement_field? [duplicate]

Question

I am attempting to use str.format() for report headers (i.e., columns) with variable widths, but I can't seem to do it using an int variable:

hlist =['h1','h2','h3','h4']
width = 7

for i in range(len(hlist)):
    # print(hlist[i].center(width), end='  ')       # this works
    print('{:^width}'.format(hlist[i]), end='  ')   # this doesn't
print()

for i in range(len(hlist)):
    # print('------'.center(width), end='  ')       # this works
    print('{:-<width}'.format('-'), end='  ')       # this doesn't
print()

Running this code gives me:

ValueError: Invalid format specifier

Using any int literal in place of width works fine. I researched here and I thought I was getting close with the format_spec arg, but it looks like it only supports non-integer formats. I tried int() as well, but no luck.

I'm happy with the solution that works using byte.center() but I was looking for a way to make use of the newer syntax for more flexibility.

Any help with this would be much appreciated!

Mad Physicist · Accepted Answer · 2016-08-02 19:43:07Z

0

You have to pass the width as a variable to the format function, and let it know that you want a variable named width, not a literal string. Since braces can be nested, do this:

hlist =['h1','h2','h3','h4']
width = 7

for i in range(len(hlist)):
    print('{:^{width}}'.format(hlist[i], width=width), end='  ')
print()

for i in range(len(hlist)):
    print('{:-<{width}}'.format('-', width=width), end='  ')
print()

answered Aug 2, 2016 at 19:43

Mad Physicist

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6 Comments

Br. Brendan Over a year ago

This is good, thank you. I'm brand new at this, but can you tell me what happened to the previous answer to this question? It seems to have been removed. I thought questions just got voted up, not removed...?

Mad Physicist Over a year ago

Not sure actually. I am guessing that the owner deleted it. I don't think it was too terrible, even if it wasn't the canonical answer, so I doubt that a moderator removed it.

Br. Brendan Over a year ago

Yes, perhaps the user did that; your answer was more to my point. I did vote up the answer, however I'm too new for my upvotes to show publicly :-\ Thanks again...

Mad Physicist Over a year ago

That's OK. Can you select the answer once the question is closed?

Br. Brendan Over a year ago

Yes, it seems I can. I receive this message after I vote an answer up : Thanks for the feedback! Votes cast by those with less than 15 reputation are recorded, but do not change the publicly displayed post score.

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