4: f-string formatting
- Page ID
- 431770
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)f-strings are the most recent and easiest way to format output, and so we will cover them first. You simply place an f in front of the quotes, and use curly brackets to insert variable names.
- Introduced in Python 3.6
- Place f in front of string
- allows you to skip the .format() step
Analyze the code, then run it, and then answer the questions below it.
Exercise \(\PageIndex{15.a}\)
Answer the following questions concerning the above code
- Which variable is a string?
- Which variable is an integer?
- Which variables are floats?
- What does \ do?
- What does \n do?
- What does \t do?
- Answer a
- molecule
- Answer b
- mass
- Answer c
- molar mass and moles, which is an integer divided by a float
- Answer d
- Allows you to extend a long line of python script to the next line (this f-string is very long). The best practice is not to have a line of code longer than 80 characters.
- Answer e
- Next line (like the carriage return on a typewritter)
- Answer f
- tab
Note that we often want to limit the number of digits displayed to the right of the decimal to represent the precision with which a number is known. In the following example we will try and show how this is done for f-strings. we first print 20 decimal digits, so you can see what position a number is printed, and then we print the variable twice, using different format conventions
Exercise \(\PageIndex{1}\)
consider the expression {variable_name:xx.yyf}
- What does the colon indiate?
- What does the xx indicate?
- What does the yy indicate?
- What does the f indicate?
- Answer a
-
The colon indicates the following statement describes the formatting of the variable in the print statement
- Answer b
-
This tells you the width of the number. This allows you to right justify all numbers.
- Answer c
-
This tells you the precision of the number, that is, how many values to the right of the decimal are expressed in the print statement
- Answer d
-
this is a floating decimal number
Exercise \(\PageIndex{15.a}\)
Consider the following code and answer question (a) before running it
- The :2.3f has a width of 2 and a precision of 3, so how long will the number be printed out?
- Which variable is an integer?
- Which variables are floats?
- What does \ do?
- What does \n do?
- What does \t do?
- Answer a
- The entire number will be printed to the third decimal, so 8 characters including the dot.
- Answer b
- mass
- Answer c
- molar mass and moles, which is an integer divided by a float
- Answer d
- Allows you to extend a long line of python script to the next line (this f-string is very long). The best practice is not to have a line of code longer than 80 characters.
- Answer e
- Next line (like the carriage return on a typewritter)
- Answer f
- tab