Python decimal to string format

Convert Float to String in Python

In this blog, we will learn how to convert float to string in Python with this comprehensive guide. Explore various methods such as str(), format(), f-strings, repr(), % operator, and the decimal module, along with examples and explanations.

Introduction:

In Python, data types such as integers, floating-point numbers, and strings are widely used in programming. Often, there is a need to convert one data type to another for various purposes, such as data manipulation, input/output handling, and data formatting. Converting a float to a string is a common operation in Python, and there are several methods available to achieve this task. In this blog, we will explore various methods to convert a float to a string in Python, with examples and explanations for each method.

Let’s start by discussing the different methods available to convert a float to a string in Python:

1. Using the str() Function:

The simplest and most straightforward way to convert a float to a string is by using the str() function, which is a built-in function in Python. The str() function takes a single argument, which is the float value that needs to be converted to a string. Here’s an example:

# Using the str() function float_num = 3.14 str_num = str(float_num) print(str_num) 

Output:

In the above example, the str() function is used to convert the float value 3.14 to a string. The resulting string ‘3.14’ is stored in the variable str_num . The print() function is then used to display the converted string value.

2. Using the format() Method:

Another way to convert a float to a string in Python is by using the format() method, which is a built-in method available for string objects. The format() method allows you to format a string by inserting values into placeholders. Here’s an example:

# Using the format() method float_num = 3.14 str_num = "<>".format(float_num) print(str_num) 

Output:

In the above example, the format() method is used to insert the float value 3.14 into the placeholder <> in the string. The resulting string ‘3.14’ is stored in the variable str_num , and the print() function is used to display the converted string value.

3. Using f-strings:

Introduced in Python 3.6, f-strings provide a concise and readable way to format strings with embedded expressions. You can use f-strings to directly convert a float to a string by including the float value inside the curly braces <> . Here’s an example:

# Using f-strings float_num = 3.14 str_num = f"" print(str_num) 

Output:

In the above example, the float value 3.14 is directly included inside the f-string, which is enclosed in the curly braces <> . The resulting string ‘3.14’ is stored in the variable str_num , and the print() function is used to display the converted string value.

4. Using the repr() Function:

The repr() function is another built-in function in Python that can be used to convert a float to a string. The repr() function returns a string that represents the printable version of an object. Here’s an example:

# Using the repr() function float_num = 3.14 str_num = repr(float_num) print(str_num) 

Output:

In the above example, the repr() function is used to convert the float value 3.14 to a string. The resulting string ‘3.14’ is stored in the variable str_num , and the print() function is used to display the converted string value.

5. Using the % Operator:

The % operator in Python is used for string formatting and can also be used to convert a float to a string. This method is similar to the one used in C’s printf function. Here’s an example:

# Using the % operator float_num = 3.14 str_num = "%s" % float_num print(str_num) 

Output:

In the above example, the %s is a placeholder that represents a string in the string format, and the % operator is used to replace the placeholder with the float value 3.14 . The resulting string ‘3.14’ is stored in the variable str_num , and the print() function is used to display the converted string value.

6. Using the decimal Module:

The decimal module in Python provides support for fast correctly rounded decimal floating-point arithmetic. This module can also be used to convert a float to a string with specific formatting options, such as precision and rounding. Here’s an example:

# Using the decimal module from decimal import Decimal float_num = 3.14 str_num = Decimal(float_num).to_eng_string() print(str_num) 

Output:

In the above example, the Decimal class from the decimal module is used to create a decimal object from the float value 3.14 , and the to_eng_string() method is used to convert the decimal object to a string representation. The resulting string ‘3.14’ is stored in the variable str_num , and the print() function is used to display the converted string value.

Conclusion:

In this blog, we explored various methods to convert a float to a string in Python. We covered methods such as using the str() function, the format() method, f-strings, the repr() function, the % operator, and the decimal module. Each method has its own advantages and can be used depending on the specific requirements of the task at hand. It is essential to choose the appropriate method based on factors such as ease of use, performance, and formatting options.

In conclusion, converting a float to a string in Python is a simple but crucial operation in many programming scenarios. By understanding the different methods available and their usage, you can effectively convert float values to string representations in your Python programs.

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String Formatting

Python v2.7 introduced a new string formatting method, that is now the default in Python3. I started this string formatting cookbook as a quick reference to help me format numbers and strings. Thanks to other contributors I’ve expanded the examples over time.

Python 3.6 introduced, formatted string literals, often referred to as f-strings as another method to help format strings. It is simpler to prepend an f to the string then append .format() . Using f-strings in Python is similar to JavaScript’s template literals, if you are familiar with them.

Here’s an example comparing the three ways to format a float number:

pi = 3.14159 print(" pi = %1.2f " % pi) # older print(" pi = ".format( pi )) # .format() print(f" pi = pi:.2f>") # f-string 

Number formatting

This table shows various ways to format numbers using Python’s str.format() and formatted string literals, including examples for both float formatting and integer formatting.

To run examples use: print(f»») or print(«».format(NUM));

Number	Format	Output	Description
3.1415926		3.14	Format float 2 decimal places
3.1415926		+3.14	Format float 2 decimal places with sign
-1		-1.00	Format float 2 decimal places with sign
2.71828		3	Format float with no decimal places
5	2d>	05	Pad number with zeros (left padding, width 2)
5		5xxx	Pad number with x’s (right padding, width 4)
1000000		1,000,000	Number format with comma separator
0.25		25.00%	Format percentage
1000000000		1.00e+09	Exponent notation
13		13	Right aligned (default, width 10)
13		13	Left aligned (width 10)
13		13	Center aligned (width 10)

String .format() basics

Here are a couple of examples of basic string substitution, the <> is the placeholder for substituted variables. If no format is specified, it will insert and format as a string.

s1 = "show me the <>".format("money") s2 = "hmmm, this is a <> <>".format("tasty", "burger") 

With formatted string literals, this is simply:

s1 = f"show me the money>" s2 = f"hmmm, this is a tasty> burger>" 

Substitution positioning

One benefit of .format() that is not available in f-strings is using the numeric position of the variables and change them in the strings, this gives some flexibility when doing the formatting, if you make a mistake in the order you can easily correct without shuffling all the variables around.

s1 = "  is better than  ".format("emacs", "vim") s2 = "  is better than  ".format("emacs", "vim") 

Variable formatting

You can use <> as a variable inside the formatting brackets (h/t Peter Beens for tip). This example uses a precision variable to control how many decimal places to show:

pi = 3.1415926 precision = 4 print( "<>f>".format( pi, precision ) ) >>> 3.1415 

Older % string formatter

An example comparing variable substitution with the older % method vs. .format() :

s1 = "cats" s2 = "dogs" s3 = " %s and %s living together" % (s1, s2) s4 = " <> and <> living together ".format(s1, s2) 

Using the older format method, I would often get the errors:

TypeError: not enough arguments for format string 

TypeError: not all arguments converted during string formatting 

because I miscounted my substitution variables, doing something like the following made it easy to miss a variable.

Using one of the new Python string formatters you can use numbered parameters so you don’t have to count how many you have, at least on half of it.

set = " ( , , , , , , , ) ".format(a,b,c,d,e,f,g) 

Formatted string literals

As shown above, formatted string literals, or f-strings, use a shorter syntax making it easier and more template-like. F-strings also support functions inside of the brackets < >this allows you to:

Do math with f-strings:

print( f"Do math: 3 * 6 = 3 * 6>" ) >>> Do math: 3 * 6 = 18 

Call functions with f-strings;

verb = "runs" print( f"The girl verb.upper()> quickly." ) >>> The girl RUNS quickly. 

Delimiting f-strings

You can use f-strings using the three different type of quotation marks in Python, single, double, or triple quotes. The following will all output the same:

name = "Fred" print( f'name>' ) print( f"name>" ) print( f"""name>""" ) 

F-String error

The one thing you’ll want to be careful is mixing the two formats, if you try to use <> inside of an f-string, you will get the error:

SyntaxError: f-string: empty expression not allowed 

Each set of brackets used in an f-string requires a value or variable.

Formatting tips with .format()

The format() function offers additional features and capabilities, here are a few useful tips and tricks to format strings in Python:

Reuse same variable multiple times

Using % to format requires a strict ordering of variables, the .format() method allows you to put them in any order as well as repeating for reuse.

"Oh , ! wherefore art thou ?".format("Romeo") >>> 'Oh Romeo, Romeo! wherefore art thou Romeo?' 

Convert values to different bases

A surprising use, you can use the string format command to convert numbers to different bases. Use the letter in the formatter to indicate the number base: decimal, hex, octal, or binary.

This example formats the number 21 in each base:

"  -  -  -  ".format(21) >>> 21 - 15 - 25 - 10101 

Use format as a function

You can use .format as a function to separate text and formatting from code. For example, at the beginning of your program include all your formats for later use.

## defining formats email_f = "Your email address was ".format ## use elsewhere print(email_f(email="bob@example.com")) 

Hat tip to earthboundkids who provided this on reddit.

Using format as a function can be used to adjust formating by user preference.

## set user preferred format num_format = " ".format ## use elsewhere print(num_format(1000000)) 

Internationalization

To use locale specific formatting for numbers, you need to first set the locale, and then use the formating code n instead of d . For example, using commas or periods to separate thousands in numbers based on the user’s locale.

Here is an example, setting locale and formatting a number to display the proper separator:

import locale locale.setlocale(locale.LC_ALL, '') print(" ".format(1000000)) 

Escaping braces

If you need to use braces when using str.format() just double them up:

print(" The <> set is often represented as % raw %>>% endraw %>".format("empty")) ~~ The empty set is often represented as 0> 

Table formatting data

Use the width and the left and right justification to align your data into a nice table format. Here’s an example to show how to format:

# data starters = [ [ 'Andre Iguodala', 4, 3, 7 ], [ 'Klay Thompson', 5, 0, 21 ], [ 'Stephen Curry', 5, 8, 36 ], [ 'Draymon Green', 9, 4, 11 ], [ 'Andrew Bogut', 3, 0, 2 ], ] # define format row row = "|  |  |  |  |".format for p in starters: print(row(player=p[0], reb=p[1], ast=p[2], pts=p[3])) 

 | Andre Iguodala | 4 | 3 | 7 | | Klay Thompson | 5 | 0 | 21 | | Stephen Curry | 5 | 8 | 36 | | Draymon Green | 9 | 4 | 11 | | Andrew Bogut | 3 | 0 | 2 | 

Resources

• Python String Library – Standard Library Documentation
• My Python Argparse Cookbook – examples parsing command-line arguments
• My Python Date Formatting — examples working with Python dates.

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