python string formatting fixed width

问题

I want to put a bunch of floating point numbers into a fixed-width table. That is, I want a maximum of 12 characters used. I want a minimum of 10 decimals used (if available); however, if 10 decimals makes it take up more than 12 characters, then round. My original thought was to try something like this

# I only want 12 characters used total

num1 = 0.04154721841
num2 = 10.04154721841

# not what I want
print "{:<12.11g}".format((num1))
# what I want
print "{:<12.10f}".format((num1))

# not what I want
print "{:<12.10f}".format((num2))
# what I want
print "{:<12.11g}".format((num2))

There has to be a way to achieve this without writing a function to check every number and give formatting based on the above conditions. What am I missing?

回答1:

I'm not sure this is what you are looking for, since it's not accomplished entirely with the format string, however, you could just use string slicing to lop-off the trailing chars when things get too long:

num1 = 0.04154721841
num2 = 10.04154721841
num3 = 1002.04154721841

print "{0:<12.11g}".format(num1)[:12]
print "{0:<12.11g}".format(num2)[:12]
print "{0:<12.11g}".format(num3)[:12]

outputs:

0.0415472184
10.041547218
1002.0415472

Beyond that, I'd say you should just write a function, though I'm not an expert on the str.format stuff, so I may be missing something.

来源：https://stackoverflow.com/questions/8424474/python-string-formatting-fixed-width