Nonempty format string passed to objectformat


string.format() in Python

The string. format() method of the string class in Python returns a formatted string. This is done by specifying the positions of replacement fields in the format string. The string. format() method is available in Python 2.6 and newer versions.

Use cases

The string. format() method in Python is used to format a string with placeholder values. The placeholder values are enclosed in curly brackets {}.

This method can be used in multiple ways:

-to insert user-defined values into a string
-to insert dynamic values into a string (e.g., the current date or time)
-to crop or truncate a string to a given length

Here are some examples of how to use string.format():

insert a user-defined value into a string

name = “John” # user’s name
print(“Hello, {}!”.format(name)) # prints “Hello, John!”

insert the current date and time into a string

import datetime # import the datetime module
date_and_time = datetime.datetime.now() # get the current date and time
print(“The date and time is {}.”.format(date_and_time))

prints “The date and time is 2016-03-21 12:53:59.”

Syntax

The syntax of the string.format() method is:

string.format(*args, **kwargs)

Here, *args and **kwargs in string.format() are called format specification mini-language. It contains format specifiers starting with % which refers to the next argument in line (works only one argument per specifier). For example, if we have a Python list of strings i.e.

alist = [‘red’, ‘green’, ‘blue’]
Then,

%s refers to the first element of list i.e. ‘red’ (works only for strings)
%d refers to the second element of list i.e. 1 (works only for integers)
%f refers to the third element of list i.e 2.56 (works only for floating point numbers)

Format strings

A format string is a template used to specify how the argument values are presented in the output. Python uses curly braces as the delimiters which are replaced by the actual values. The format string contains holes called conversion fields, into which the corresponding arguments are inserted.

Format string syntax


The following syntaxes are supported for format strings:

{} – placeholder for a single object.

{n} – placeholder for the nth object in the list of objects. This allows you to reorder or repeat objects in the output.

{name} – placeholder for an object’s “name” property. The name property is defined as either the object’s id property, or if that doesn’t exist, its index in the list of objects.

{#n} – same as {n}, but the output will also include the object’s “name” property.

You can also use “if” and “else” statements to conditionally include or exclude objects from the output:

{if foo > 10}  
    bar  
{else if foo > 5}  
    baz  
{else}  
    qux  
{/if}</p><br /><h3>Format string semantics</h3><br /><p>

In computer programming, a format string is a template used by various software to present data. A format string defines how the data is to be presented. It may include literal text, escape sequences, and format specifiers. A format string is sometimes called a external fmt because it represents a (potentially) constant string stored outside of the program’s code.

A format string may be either a literal string or stored in a variable. If stored in a variable, the contents of the variable may be changed at runtime, which can be used to dynamically generate different output based on changing conditions. For example, a programs that generates HTML pages may use a format string containing the HTML code for a page’s initial header and closing tags; the rest of the page’s content would be generated based on user input or other data sources.

A common use of format strings is for security-sensitive input such as passwords or credit card numbers; in these cases, the format string should contain only characters that are absolutely necessary for the desired output, and all other characters should be escaped or removed. Another common use is for generating readable output from data structures that would otherwise be difficult to interpret; in this case, the format string would likely contain field names and other annotations to make the output more understandable.

Format strings are commonly used in many programming languages; some languages have specific syntax for indicating that a given string should be interpreted as a format string, while others do not. In some cases, such as when using the printf() function in C, theformat string itself may contain formatting directives that control how subsequent arguments are to be formatted and displayed.

Object format strings

If you have ever seen a message like “nonempty format string passed to object.format”, it is because you are trying to use the format string of an object on a different object. This is not possible, and will result in this error message.

Use cases

There are three primary use cases for Python’s object format strings: -To put together a string composed of other strings -To format values for use in another string -To print() to the console or a file

Syntax

A string may be any sequence of zero or more characters enclosed in single quotes (‘), double quotes (“), or triple quotes (”’ or “””).

A character may be an ordinary character, a special character, or a escape sequence.

An ordinary character is any character that is not a special character. Ordinary characters include all letters (upper- and lower-case), all digits, and all punctuation marks. A space is also an ordinary character.

The backslash () character is used to introduce special characters and escape sequences. A special character is one that has a meaning different from its literal meaning, such as the newline character (\n) or the tab character (\t). An escape sequence is used torepresent a special or non-printable characters. For example, \r represents the carriage return character, which moves the cursor back to the beginning of the current line.

Strings may span multiple lines. For example:

print('this\nis\na\ntest')

will print:

this
is
a  <-- notice the space here!
test</p><br /><h3>Semantics</h3><br /><p>

The String.Format method returns a formatted string. The format string consists of zero or more format items, which are placeholders for optional arguments. Each format item contains the following components:

Aesthetics argument
Optional alignment component
Optional format string component
The Aesthetics argument is an object that supplies the value to be formatted. The Alignment component is an optional integer that specifies the alignment of the format item within the formatted string; it can be positive (left-aligned) or negative (right-aligned). The Format String component is an optional string that specifies how the value should be formatted; it can include standard numeric format strings or custom formats.

Examples

nonempty_format_string.upper() # ‘HELLO WORLD’

Format strings


You can use a format string as an argument to the objectFormat function. The format string consists of zero or more positional specifiers followed by optional named specifiers. A positional specifier defines the format of the next object in the list, while a named specifier defines the format of an object whose key is given by name.

Positional specifiers start with a percent sign and optionally include flag characters, width specifiers, precision specifiers, and type specifiers in that order. For example:

‘%d’ // flag characters: none
// width specifier: none
// precision specifier: none
// type specifier: d (decimal integer)
‘%20s’ // flag characters: none
// width specifier: 20 (minimum number of characters)
// precision specifier: none
// type specifier: s (string)
‘%.2f’ // flag characters: none
// width specifier: none
// precision specifier: 2 (number of digits after the decimal point)
// type specifier: f (floating-point number)

Object format strings

In Python, you can use %-formatting to create strings that include values from variables. This is often referred to as “string interpolation”. The %-operator is used for this purpose.

The %-operator can be used with any of the following type specifiers:
d – decimal integer [010203…]
i – signed decimal integer [-200…0…200]
u – unsigned decimal integer [0010203040506070809101112…]
o – octal integer [01234567…]
x – hexadecimal lowercase integer [0x0123456789abcdef…]
X – hexadecimal uppercase integer [0X0123456789ABCDEF…]
e – floating point exponential format [-4.56e+78]
E – floating point exponential format [-4.56E+78], uppercase E converts exponent to uppercase [-4.56E+78]
f – floating point decimal format [-123.456],’f’ ignores trailing zeros after the decimal point, defaults to six decimals [-123.456000]
F – floating point decimal format [-123.456], ‘F’ ignores trailing zeros after the decimal point, defaults to six decimals [-123.456000], uppercase F converts minus sign to uppercase [−123.456000] g – same as “e” if exponent is greater than -4 or less than precision, “f” otherwise Convert a float number to a string formatted in dollar currency representation:

>>> print('%0.2f' % 12345)  # two digits after the decimal point
12345.00    
>>> print('%-0.2f' % 12345) # left justify, two digits after deciminal point</p>

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