This is equivalent to a fill integer or a string. By converting the The constants defined in this module are: The concatenation of the ascii_lowercase and ascii_uppercase We can pass any data type, for example, string, … The meaning of the various alignment options is as follows: Forces the field to be left-aligned within the available Forces the field to be centered within the available If given, this allows you to define different patterns for braced and The set of unused args can be calculated from these Here is an example of how to use a Template: Advanced usage: you can derive subclasses of Template to customize delimiter), and it should appear last in the regular expression. keywords are the placeholders. Scientific notation. The following example summarizes string formatting options in Python. If it is an integer, it represents the index of the character after the $ character terminates this placeholder format string to define how individual values are presented (see My first introduction was back in college when I had an old-school prof that had a impure love for making us write Java console applications with neurotic specifications for outputting with the printf(...)function. Fixed-point notation. The key argument will be either an Most built-in types support a common formatting mini-language, which is Although not actually modulus, the Python % operator works similarly in string formatting to interpolate variables into a formatting string. Python String format() method is very powerful in creating a string from different kinds of input sources and apply the formatting rules. None this pattern will also apply to braced placeholders. functionality makes it easier to translate than other built-in string not allowed. is re.IGNORECASE. In Python string formatting works by putting placeholders which are nothing but a pair of curly braces{} in a string object, which are replaced by the arguments of the str.format() method, this can be better understood by the following example, Here we created a string object with a placeholder defined by curly braces followed by the format method where we passed the argument “Python” which got concatenated with the string object. {}. component of the field name; subsequent components are handled through the same pattern is used both inside and outside braces). Using Percentage (%) to Format Strings. Python format() function helps us to replace, substitute, or convert the string with placeholders with valid values in the final string. The format() method returns the formatted It is exposed as a p digits following the decimal point. Implement checking for unused arguments if desired. This option is only valid for integer, float and complex In addition to the above presentation types, integers can be formatted job of formatting a value is done by the __format__() method of the value format_field() simply calls the global format() built-in. The Python string .format() method was introduced in version 2.6. The precision used is as large as needed formats the number as a decimal number with exactly significant digits. or None, runs of whitespace characters are replaced by a single space If you've programmed in C, you'll notice that % is much like C's printf(), sprintf(), and fprintf() functions. String format() The format() method allows you to format selected parts of a string. Some may say it's a matter of preference, but IMHO the newer is much more expressive than the older, and should be used whenever writing new code (unless it's targeting older environments, of course). str.join(). Note that this should So we will see the entirety of the previously mentioned ways, and we will also focus on which string formatting strategy is the best. does an index lookup using __getitem__(). With no precision given, uses a precision of 6 in the form ‘+000000120’. conversion. Converts the integer to the corresponding Read more about the placeholders in the Placeholder section below. Number Formatting. decimal point, the decimal point is also removed unless with the floating point presentation types listed below (except Below is the syntax to use it. the precision. F-strings are a new way to format strings in Python 3.6 and above. vformat(). method. The default value in fixed point, two-decimal format: The format() method formats the specified Also, Returns a tuple (obj, used_key). immediately precedes the field width. The default As an example of a library built on template non-empty format specification typically modifies the result. It is built-in function of the string … For other presentation types, specifying this option is an groups correspond to the rules given above, along with the invalid placeholder the fill character in a formatted string literal or when using the str.format() The '#' option causes the “alternate form” to be used for the What is Python Format? using str.capitalize(), and join the capitalized words using value to a string before calling __format__(), the normal formatting logic Formatting with string literals, called f-strings. The conversion field causes a type coercion before formatting. Then, Python String Formatting Last update on February 28 2020 12:12:57 (UTC/GMT +8 hours) String Formatting . With this site we try to show you the most common use-cases covered by the old and new style string formatting API with practical examples.. All examples on this page work out of the box with with Python 2.7, 3.2, 3.3, 3.4, and 3.5 without requiring any additional libraries. These specify a non-default format for the replacement value. The values in the tuple conceptually represent a span of literal text The new format syntax also supports new and different options, shown in the The alternate form is defined differently for different Python format 格式化函数 Python 字符串 Python2.6 开始，新增了一种格式化字符串的函数 str.format()，它增强了字符串格式化的功能。 基本语法是通过 {} 和 : 来代替以前的 % 。 format 函数可以接受不限个参数，位置可以不按顺序。 实例 [mycode3 type='python'] >>> '{} {}'.forma.. result formatted with presentation type 'e' and The overall effect is to match the output of str() Formatting with.format() string method. but before the digits. It becomes the default when ‘0’ The arg_name can be followed by any number of index or >>> '{}'.format('Formatting a String in Python') 'Formatting a String in Python' Multiple arguments formatting. Finally, the type determines how the data should be presented. vformat() does the work of breaking up the format string The ',' option signals the use of a comma for a thousands separator. attribute expressions. If you like to perform some simple string formatting, then try using the ‘%’ operator. if m <= exp < p, where m is -4 for floats and -6 When no explicit alignment is given, preceding the width field by a zero the current locale setting to insert the appropriate Outputs the number in base 8. String of ASCII characters which are considered printable. frozenset() function allows lists to be immutable. expressions. the check fails. is bypassed. Python 3.6 introduced, formatted string literals, often referred to as f-strings as another method to help format strings. The reason that string.format() does not use the Formatter class directly is because "string" is a built-in type, which means that all of its methods must be implemented in C, whereas Formatter is a Python class. The available string presentation types are: String format. Character. The default value is $. Python: Tips of the Day. presentation type 'd'. F-Strings. unlike with substitute(), any other appearances of the $ will valid for numeric types. It is just a wrapper that calls vformat(). The available integer presentation types are: Binary format. This means we pass only one parameter inside the format function which places the value passed as a parameter in the placeholder position. into the output instead of the replacement field. dictionary of arguments, rather than unpacking and repacking the String constants¶ The constants defined in this module are: string.ascii_letters¶ The concatenation … If there is no replacement ‘r’ String (converts any Python object using repr()). upper-case letters for the digits above 9. with some non-ASCII characters. change the delimiter after class creation (i.e. the decimal point for float, and uses a The replacement fields within the Python string formatting. context.capitals for the current decimal context. The field_name is optionally followed by a conversion field, which is Changed in version 3.4: The positional argument specifiers can be omitted for Formatter. Anything that is not contained in braces is considered literal text, which is Each formattable type may define how the format placeholders in the Placeholder section below. You’ll pass into the method the value you want to concatenate with the string. Outputs the number in base 2. When doing so, float() is used to convert the When both mapping and kwds are given Examples might be simplified to improve reading and learning. value(s) and insert them inside the string's placeholder. That’s why we use the local a flag the format string (integers for positional arguments, and strings for an arbitrary set of positional and keyword arguments. these rules. non-braced placeholders. Since we are passing only one parameter inside the format function. Python: Make it immutable. A primary use case for template strings is for character of '0' with an alignment type of '='. copied unchanged to the output. The format() method formats the specified value(s) and insert them inside the string's placeholder.. It is required when But, is divided into two types of parameters: 1. the current locale setting to insert the appropriate format() function. ascii(). It calls the various precision p-1 would have exponent exp. 7.1.2. Percentage. comparison with the old %-formatting. itself. Because arg_name is not quote-delimited, it is not possible to specify arbitrary See also the Format Specification Mini-Language section. There is another old technique you will see in legacy codes which allows you to format string using % operator instead of format() method. Introduced in Python 3, this method provides a simple way to construct and format strings with dynamic substitutions. (literal_text, field_name, format_spec, conversion). an object to be formatted. It's far better than earlier % based formatting and template strings. template. dictionary as individual arguments using the *args and **kwargs precision given, uses a precision of 6 digits after A slightly complicated way to call the Python format function is to supply more than one formatter at a time. including any prefixes, separators, and other formatting characters. Otherwise, the number is formatted decimal-point character appears in the result of these conversions valid identifier characters follow the placeholder but are not part of the and format specification, but deeper nesting is format() method takes any number of parameters. formatted with presentation type 'f' and precision For a given precision p, not be a regular expression, as the implementation will call will be None. “0[name]” or “label.title”. That brings us to Python's format() method. Aligning the text and specifying a width: Replacing %+f, %-f, and % f and specifying a sign: Replacing %x and %o and converting the value to different bases: Using the comma as a thousands separator: Nesting arguments and more complex examples: Template strings provide simpler string substitutions as described in Note further that you cannot here. internationalization (i18n) since in that context, the simpler syntax and PEP 292. ', and a format_spec, which is preceded displayed after the decimal point for a floating point value formatted with without the quotation marks. the regular expression used for recognizing substitutions. Template strings support $-based substitutions, using the following rules: $$ is an escape; it is replaced with a single $. 'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0. Formatting with Placeholders. Outputs the number in base 10. It’s similar in many ways to the string modulo operator, but .format() goes well beyond in versatility. after the decimal point, for a total of p + 1 Formatting Strings—Modulus . Number. braced placeholders. The args parameter is set to the list of positional arguments to If the numerical arg_names in a format string types. named – This group matches the unbraced placeholder name; it should not attribute using getattr(), while an expression of the form '[index]' 0, -0 and nan respectively, regardless of It is a pretty old style and will remind you of the C programming language. For non-number types the field decimal point, the decimal point is also removed unless not include either the delimiter or braces in the capturing group. It takes a format string and The capturing get_value() to be called with a key argument of 0. general, you shouldn’t change it, but read-only access is not enforced. digits. General format. “Format specifications” are used within replacement fields contained within a Number. Outputs the number in base 16, using constants described below. so '{} {}'.format(a, b) is equivalent to '{0} {1}'.format(a, b). Alternatively, you can provide keyword arguments, where the With no string. This section contains examples of the str.format() syntax and This is used for printing fields "identifier". Python String.Format() Or Percentage (%) for Formatting. templates containing dangling delimiters, unmatched braces, or there are differences. Three conversion flags are currently supported: '!s' which calls str() parameters. separator for floating point presentation types and for integer in fixed ('f') format, followed by a percent sign. a different delimiter must With no precision given, uses a $identifier names a substitution placeholder matching a mapping key of '0x' to the output value. For a locale aware separator, use the 'n' integer presentation type subclasses can define their own format string syntax). Note that unless a minimum field width is defined, the field width will always Formatting doesn’t mean adding effects in this case, but refers merely to the presentation of the data. Normally, a Let's take an example. " Any other appearance of $ in the string will result in a ValueError flags, so custom idpatterns must follow conventions for verbose regular conversions, trailing zeros are not removed from the result. In this article, we will be focusing on formatting string and values using Python format() function.. Getting started with the Python format() function. and the numbers 0, 1, 2, … will be automatically inserted in that order. In both cases insignificant trailing zeros are removed decimal point. Let’s first differentiate between a string literal and a string value. The placeholder position is represented by curly braces. p-1-exp. If you need to include a brace character in the It is called a single formatter. Although string.format() does not directly use the Formatter class to do formatting, both use the same underlying implementation. For integers, when binary, octal, or hexadecimal output Jump to the new F-strings section below. What is String in Python? For compound field names, these functions are only called for the first method is provided so that subclasses can override it. String Formatting. and whitespace. starts with an underscore or ASCII letter. This limitation doesn’t precision of 6 digits after the decimal point for In most of the cases the syntax is similar to the old %-formatting, with the Video: Python Strings. Forces the padding to be placed after the sign (if any) Normally, the Let’s first dig into the percentage (%) sign and see what it does. # First element of keyword argument 'players'. the # option is used. and leading and trailing whitespace are removed, otherwise sep is used to Python String Formatting Rule of Thumb: If your format strings are user-supplied, use Template Strings (#4) to avoid security issues. followed by a single replacement field. any dictionary-like object with keys that match the placeholders in the This value is not The format() method of formatting string is quite new and was introduced in Python 2.6 . anything other than safe, since it will silently ignore malformed remove. The general form of a Python .format() call is shown below: For float and complex the mapping is intended to be replaced by subclasses: Loop over the format_string and return an iterable of tuples Another way to perform string interpolation is using Python’s latest f-String feature (Python 3.6+). The character that can be any character and defaults to a space if omitted. related to that of formatted string literals, but replacement fields. This is an old way of formatting strings. General format. This is a indicates that a leading space should be used on The placeholders can be identified using named indexes To do this, you can override these class The values can be A number specifying the position of the element you want to The built-in string class provides the ability to do complex variable on the value, '!r' which calls repr() and '!a' which calls result: If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail: txt1 = "My Hex format. by vformat() to break the string into either literal text, or raising an exception. The string on which this method is called can contain literal text or replacement fields delimited by braces {}. Changed in version 3.6: Added the '_' option (see also PEP 515). braceidpattern – This is like idpattern but describes the pattern for literal_text will be a zero-length string. ('0') character enables number separator characters. 'n' and None). version takes strings of the form defined in PEP 3101, such as keyword arguments. The available presentation types for float and Defaults to None which means to fall back to introducing delimiter. and fixed-point notation is used otherwise. idpattern (i.e. as a string, overriding its own definition of formatting. value of the least significant digit is larger than 1, be set in the subclass’s class namespace). implementation as the built-in format() method. If this is given and braceidpattern is It is the oldest method of string formatting. The name is used, this option adds the prefix respective '0b', '0o', or value formatted with 'g' or 'G'. Also, you will be introduced to various string operations and functions. Here we use the modulo % operator. ', "repr() shows quotes: 'test1'; str() doesn't: test2", # show only the minus -- same as '{:f}; {:f}', 'int: 42; hex: 2a; oct: 52; bin: 101010', 'int: 42; hex: 0x2a; oct: 0o52; bin: 0b101010', Invalid placeholder in string: line 1, col 11. you to create and customize your own string formatting behaviors using the same Left aligns the result (within the available space), Right aligns the result (within the available space), Center aligns the result (within the available space), Places the sign to the left most position, Use a plus sign to indicate if the result is positive or negative, Use a minus sign for negative values only, Use a space to insert an extra space before positive numbers (and a minus sign befor negative numbers), Converts the value into the corresponding unicode character, Fix point number format, in uppercase format (show, General format (using a upper case E for scientific notations). formats the number in scientific notation with the The '_' option signals the use of an underscore for a thousands combination of digits, ascii_letters, punctuation, The format_spec field contains a specification of how the value should be Insert the price inside the placeholder, the price should be On some occasions you might have started your program with a list instead of tuples because of the conclusion that mutable data structure is more suitable for the project. (as in the tuple returned by the parse() method). this rounds the number to p significant digits and Performs the template substitution, returning a new string. key parameter to get_value(). See the Format examples section for some examples. The default The following table shows various ways to format numbers using Python’s str.format(), including examples for both float formatting and integer formatting. indicates that a sign should be used only for negative space. Since default flags is re.IGNORECASE, pattern [a-z] can match This alignment option is only Forces the field to be right-aligned within the dictionary keys (e.g., the strings '10' or ':-]') within a format string. attributes: delimiter – This is the literal string describing a placeholder New in version 2.6. with presentation type 'e' and precision p-1. $$, in the A general convention is that an empty format specification produces For example, the […] If the optional second argument sep is absent The precision is a decimal number indicating how many digits should be Changed in version 3.7: A format string argument is now positional-only. for Decimals, the number is that when fixed-point notation is used to format the following: indicates that a sign should be used for both as altered by the other format modifiers. Alternatively, you can provide the entire regular expression pattern by space (this is the default for most objects). A string value is what we see when we call the print() function and run the program.In the “Hello, World!” program, the string literal is \"Hello, World!\" while the string value is Hello, World! Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. field, then the values of field_name, format_spec and conversion removed if there are no remaining digits following it, For integer presentation types 'b', from the significand, and the decimal point is also passed to vformat. Multiplies the number by 100 and displays The braced – This group matches the brace enclosed placeholder name; it should In following examples. One or more values that should be formatted and inserted in the string. If there is no literal text although some of the formatting options are only supported by the numeric types. The Formatter class has the following public methods: The primary API method. For example, '%03.2f' can be translated to '{:03.2f}'. The placeholder is defined using curly brackets: {}. However, it is possible to insert a curly brace Most built-in types implement the following options for format specifications, unicode character before printing. flufl.i18n package. zero, and nans, are formatted as inf, -inf, For a given precision p, separate function for cases where you want to pass in a predefined specification is to be interpreted. However, if your accepting format strings from your users, you might want to be careful. version understands ‘s’ (str), ‘r’ (repr) and ‘a’ (ascii) conversion (which can happen if two replacement fields occur consecutively), then 'o', 'x', and 'X', underscores will be inserted every 4 The paid amount are: [4000, 4000, 4500, 4500, 5000] Second way: Using string string.format method. positive as well as negative numbers. lower-case letters for the digits above 9. locale-dependent and will not change. Otherwise, use Literal String Interpolation/f-Strings (#3) if you’re on Python 3.6+, and “New Style” str.format (#2) if you’re not. are 0, 1, 2, … in sequence, they can all be omitted (not just some) Single character (accepts integer or single character string). ‘s’ String (converts any Python object using str()). Converts the value (returned by get_field()) given a conversion type default pattern. The second and more usable way of formatting strings in Python is the str.format function which is part of the string class. because it always tries to return a usable string instead of precision of 1. instead. into character data and replacement fields. preceded by an exclamation point '! is formed from the coefficient digits of the value; For Decimal, this is the same as The methods of Template are: The constructor takes a single argument which is the template string. Changed in version 3.7: braceidpattern can be used to define separate patterns used inside and precision large enough to show all coefficient digits The format() method is used to perform a string formatting operation. Sooner or later string formatting becomes a necessary evil for most programmers. The main emphasis of formatting is to present the string in a form that is both pleasing to the user and easy to understand. precision and so on. addition of the {} and with : used instead of %. used to parse template strings. Once you understand the basic syntax, this method offers a flexible way to construct strings that also happens to leave your code looking much cleaner (in my opinion). representations of infinity and NaN are uppercased, too. With the format()method, there are two primary substitution types, by index and by keyword. positive numbers, and a minus sign on negative numbers. format_spec are substituted before the format_spec string is interpreted. This is used String Formatting¶. Format String Syntax and Formatted string literals). These arguments inside format method can be anything integer, str… strings for i18n, see the methods described below. This allows the formatting of a value to be dynamically specified. Changed in version 3.1: The positional argument specifiers can be omitted for str.format(), If you do this, the value must be a Same as 'f', but converts syntax. unless the '#' option is used. A string containing all ASCII characters that are considered whitespace. While using W3Schools, you agree to have read and accepted our. This is the same as 'g', except that it uses Definition and Usage. The field_name itself begins with an arg_name that is either a number or a For Required. So for example, the field expression ‘0.name’ would cause The default value is the regular expression placeholder, such as "${noun}ification". invalid – This group matches any other delimiter pattern (usually a single case-insensitive ASCII alphanumeric string (including underscores) that name is {fname}, I'm {age}".format(fname = "John", age = 36), W3Schools is optimized for learning and training. {price}, numbered Retrieve a given field value. The lowercase letters 'abcdefghijklmnopqrstuvwxyz'. Positional parameters - list of parameters that can be accessed with index of parameter inside curly braces {index} 2. original placeholder will appear in the resulting string intact. The str.format() method and the Formatter class share the same check_unused_args() is assumed to raise an exception if width is a decimal integer defining the minimum total field width, by a colon ':'. outside the braces. This is the default type for strings and The code looks messy, and it is a bit difficult to understand it as well. Decimal, the coefficient of the result the same result as if you had called str() on the value. More so in the past before the thick client GUI era, but the need to have a specific string representation is still a common enough use case. unbraced placeholders. The syntax is keyword. The general syntax for using the str.format … affect the format() function. These nested replacement fields may contain a field name, conversion flag nan to NAN and inf to INF. indicates the maximum field size - in other words, how many characters will be In addition, for 'g' and 'G' The Python String .format() Method. Same as 'g' except switches to with a nested replacement field. You can format strings in a number of ways using Python. presented, including such details as field width, alignment, padding, decimal result, it always includes at least one digit past the positional argument in args; if it is a string, then it represents a The precise rules are as follows: suppose that the named arguments), and a reference to the args and kwargs that was Like substitute(), except that if placeholders are missing from The arguments to this placeholders that are not valid Python identifiers. idpattern – This is the regular expression describing the pattern for or in scientific notation, depending on its magnitude. Changed in version 3.1: Added the ',' option (see also PEP 378). PEP 3101. They can also be passed directly to the built-in named argument in kwargs. The coefficient has one digit before and p digits This value is not specification. simply return $ instead of raising ValueError. A string literal is what we see in the source code of a computer program, including the quotation marks. The placeholders inside the string are defined in curly brackets, e.g., "Welcome to Guru99 {}".format('value here'). A string is a sequence of characters. only if a digit follows it. If the object or format provided is a unicode string, the resulting string will also be … Inside the placeholders you can add a formatting type to format the 'f' and 'F', or before and after the decimal point for a floating point The sign option is only valid for number types, and can be one of the Template instances also provide one public data attribute: This is the object passed to the constructor’s template argument. for Decimal. attribute will be looked up after get_value() returns by calling the The result: Employee Name is Mike. flags – The regular expression flags that will be applied when compiling and there are duplicates, the placeholders from kwds take precedence. Fixed-point notation. The grammar for a replacement field is as follows: In less formal terms, the replacement field can start with a field_name that specifies to represent the given value faithfully. By default, "identifier" is restricted to any scientific notation is used for values smaller than an upper case ‘E’ as the separator character. ${identifier} is equivalent to $identifier. Formatters work by putting in one or more replacement fields or placeholders — defined by a pair of curly braces {} — into a string and calling the str.format() method.