6.10: String formatting
- Page ID
- 23726
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)In Python programming, string formatting plays a crucial role in enhancing the readability and utility of output data. Properly formatted strings help ensure that the output is clear, consistent, and easy to interpret. Consider a scenario where you're displaying floating-point numbers representing scientific measurements. Without proper formatting, you might end up with numbers like "3.141592653589793" or "0.20000000000000001," which could be cumbersome and confusing to read. On the other hand, using string formatting allows you to control the number of decimal places, so you get cleaner, more digestible outputs like "3.14" or "0.20". The ability to precisely control output styles becomes even more important in more complex applications, such as data analysis or scientific computing, where the manner in which data is presented can significantly impact the interpretation of results. Therefore, mastering string formatting is essential for anyone looking to produce high-quality, professional-level Python code.
I will now introduce f-string formatting, a modern and convenient way to format strings. By preceding a string with the letter 'f' or 'F', you can embed expressions inside string literals, enclosed by curly braces `{}`. These expressions are evaluated at runtime, and their values are directly inserted into the string. For example, if you have variables `name` and `age`, instead of the cumbersome concatenation like `"Hello, " + name + ". You are " + str(age) + " years old."`, you can simply write `f"Hello, {name}. You are {age} years old."`
The f-string method not only makes the code cleaner but also improves readability and reduces the chance of errors. You can even control the number of decimal places in a floating-point number with ease, for example, `f"The value of pi is approximately {pi:.2f}"`, which would format the value of pi to two decimal places. This brings a level of clarity and precision to your output, streamlining both development and debugging processes.
Within the string, the {}s have the variable and how it is formatted, using the syntax {variable:format}.
the format contains the following format: Width.DecimalCode. For example, you could write it as f'{dog:4.1f}'. This create the string of the value of dog, with a width of 4 spaces, and one digit after the decimal point.
dog = 3.14159
f'{dog:4.1f}'
It outputs ' 3.1', which a length of 4 and one digit after the decimal point. If you leave out the '4', it will just format the string so that there's just one digit after the decimal point.
cat = 342.38780
f'{cat:.2f}'
Outputs '342.39'
'f' is one format code, but there are others. For example, if you want the output to be in exponential notation, you can use the 'e' code:
f'{cat:.2e}'
which yields '3.42e+02'. Here is a list of formatting codes.
| Type | Meaning |
|---|---|
| d | Decimal integer |
| c | Corresponding Unicode character |
| b | Binary format |
| o | Octal format |
| x | Hexadecimal format (lower case) |
| X | Hexadecimal format (upper case) |
| n | Same as 'd'. Except it uses current locale setting for number separator |
| e | Exponential notation. (lowercase e) |
| E | Exponential notation (uppercase E) |
| f | Displays fixed point number (Default: 6) |
| F | Same as 'f'. Except displays 'inf' as 'INF' and 'nan' as 'NAN' |
| g | General format. Rounds number to p significant digits. (Default precision: 6) |
| G | Same as 'g'. Except switches to 'E' if the number is large. |
| % | Percentage. Multiples by 100 and puts % at the end. |
Read more about f-string formatting here.