The following table shows a variety of ways to format numbers with Python's rookie str.format(), including examples of floating-point number formatting and integer formatting. You can use print("FORMAT".format(NUMBER)); to run the example, so you can run: print("{:.2f}".format(3.1415926)); to get the output of the first example.
| Number | Format | Output | Description |
|---|---|---|---|
| 3.1415926 | {:.2f} | 3.14 | Two decimal places |
| 3.1415926 | {:+.2f} | +3.14 | Two decimal places with signs |
| -1 | {:+.2f} | -1.00 | Two decimal places with symbols |
| 2.71828 | {:.0f} | 3 | Without decimal points |
| 5 | {:0>2d} | 05 | Number with 0 padding(left fills, width is 2) |
| 5 | {:X<4d} | 5xxx | Number with x padding(right fills, width is 4) |
| Ten | {:X<4d} | 10xx | Number with x padding(right fills, width is 4) |
| 1000000 | {:,} | 1,000,000 | Comma based numbers |
| 0.25 | {:.2%} | 25.00% | Percentage format |
| 1000000000 | {:.2e} | 1.00e+09 | Exponent notation |
| 13 | {:10d} | 13 | Right alignment (default, width 10) |
| 13 | {:<10d} | 13 | Left alignment (width 10) |
| 13 | {:^10d} | 13 | Middle alignment (width 10) |
The following are two examples of basic string replacement. The symbol {} is the placeholder of the replacement variable. If the format is not specified, the variable value is directly inserted as a string.
S1 = "so much depends upon {}".format("a red wheel barrow")
S2 = "glazed with {} water beside the {} chickens".format("rain", "white")
You can also use the position values of variables to change them in the string, which will be more flexible when formatting. If the order is wrong, you can easily correct it without disrupting all the variables.
S1 = " {0} is better than {1} ".format("emacs", "vim")
S2 = " {1} is better than {0} ".format("emacs", "vim")
Before Python2.6, the use of format strings was relatively simpler, although the number of parameters it could receive was limited. These methods are still valid in Python 3.3, but there have been implicit warnings that these methods will be completely eliminated, and there is no clear schedule. [ PEP-3101]
Pi = 3.14159
Print(" pi = %1.2f ", % pi)
S1 = "cats"
S2 = "dogs"
S3 = " %s and %s living together" % (s1, s2)
There are not enough parameters.
Using the old formatting method, I often make mistakes in "TypeError: not enough arguments for formating string" because I miscount the number of replacement variables. It is easy to miss variables when writing the following code. .
Set = (%s, %s, %s, %s, %s, %s, %s, %s) " % (a,b,c,d,e,f,g,h,i)
For new Python format strings, you can use numbered parameters, so that you don't need to count how many parameters there are.
Set = set = " ({0}, {1}, {2}, {3}, {4}, {5}, {6}, {7}) ".format(a,b,c,d,e,f,g)
The format() function provides quite a lot of additional features and functions. The following are some useful tips for using .format().
You can use the new format string as a template engine and use named parameters, so that a strict order is not required.
Madlib = " I {verb} the {object} off the {place} ".format(verb="took", object="cheese", place="table ")
I took the cheese off the table
Using % format strings requires variables to have a strict order, while the .format() method allows arbitrary arrangement of parameters as shown above, and also allows reuse.
Str = "Oh {0}, {0}! Wherefore art thou {0}?".format("Romeo")
Oh Romeo, Romeo! Wherefore art thou Romeo?
You can use the following letters to convert numbers into decimal, hex, octal, binary.
Print("{0:d} - {0:x} - {0:o} - {0:b} ".format(21))
21 - 15 - 25 -10101
.Format() can be used as a function, which allows ordinary text to be distinguished from the format in the code. For example, you can include all the formats you need to use at the beginning of the program, and then use them later. This is also a good way to deal with internationalization, which requires not only different texts, but also different digital formats.
Email_f = "Your email address was {email}".format
Use it in another place.
Print(email_f(email="bob@example.com"))
Thanks to earthboundkid for providing this skill on reddit.
Escasing braces
When using str.format(), if you need to use braces, just write it twice:
Print(" The {} set is often represented as { {0} } ".format("empty"))
The empty set is often represented as {0}