Formatting numbers#

Every number handcalcs shows goes through a Python format code, the part after the colon in f"{value:.2f}". The default is .5g: up to five significant figures, switching to scientific notation for very large or small values. An integer keeps all its digits under a g format code (E = 200000, not 2e+05); a code such as .2f or .3e applies to integers too. The elements of a list, tuple or numpy array each take the format code, and a two-dimensional numpy array is shown as a matrix.

a = 1234.56789
b = 0.000012345
c = a * b

Output (ASCIIRenderer)

a = 1234.6
b = 1.2345e-05
c = a * b = 1234.6 * 1.2345e-05 = 0.015241

Common format codes#

Code	Meaning	`1234.56789` becomes
`.5g`	5 significant figures (default)	`1234.6`
`.3g`	3 significant figures	`1.23e+03`
`.2f`	2 decimal places	`1234.57`
`.0f`	no decimals	`1235`
`.3e`	scientific, 3 decimals	`1.235e+03`
`,.1f`	thousands separator, 1 decimal	`1,234.6`

The LaTeX and Markdown renderers typeset scientific notation as 1.235 × 10³ rather than 1.235e+03. The same value with four codes:

x = 1234.56789 * 1         # hc: -f .5g
x_3g = 1234.56789 * 1      # hc: -f .3g
x_2f = 1234.56789 * 1      # hc: -f .2f
x_3e = 1234.56789 * 1      # hc: -f .3e

Output (MarkdownRenderer)

Rendered

\[\begin{aligned} x &= 1234.56789 \cdot 1 = 1234.6 \\ x_{\mathrm{3g}} &= 1234.56789 \cdot 1 = 1.23 \times 10^{3} \\ x_{\mathrm{2f}} &= 1234.56789 \cdot 1 = 1234.57 \\ x_{\mathrm{3e}} &= 1234.56789 \cdot 1 = 1.235 \times 10^{3} \end{aligned}\]

Markdown output

$$\begin{aligned} x &= 1234.56789 \cdot 1 = 1234.6 \\ x_{\mathrm{3g}} &= 1234.56789 \cdot 1 = 1.23 \times 10^{3} \\ x_{\mathrm{2f}} &= 1234.56789 \cdot 1 = 1234.57 \\ x_{\mathrm{3e}} &= 1234.56789 \cdot 1 = 1.235 \times 10^{3} \end{aligned}$$

Numbers you type inside a formula keep their digits as written (1234.56789 above); the format code applies to calculated values and to the values of parameters.

Where to set it#

From the narrowest scope to the widest:

One line: a command at the end of the line.

a = 2.0
b = 1 / 3
c = a * b  # hc: -f .2f
d = a * b

Output (MarkdownRenderer)

Rendered

\[\begin{aligned} a &= 2 \\ b &= \frac{1}{3} = 0.33333 \\ c &= a \cdot b = 2.00 \cdot 0.33 = 0.67 \\ d &= a \cdot b = 2 \cdot 0.33333 = 0.66667 \end{aligned}\]

Markdown output

$$\begin{aligned} a &= 2 \\ b &= \frac{1}{3} = 0.33333 \\ c &= a \cdot b = 2.00 \cdot 0.33 = 0.67 \\ d &= a \cdot b = 2 \cdot 0.33333 = 0.66667 \end{aligned}$$

The rest of the calculation: a command on its own line.

a = 2.0
b = 1 / 3
# hc: -f .3e
c = a * b
d = c / 7

Output (MarkdownRenderer)

Rendered

\[\begin{aligned} a &= 2 \\ b &= \frac{1}{3} = 0.33333 \end{aligned}\]

\[\begin{aligned} c &= a \cdot b = 2.000 \times 10^{0} \cdot 3.333 \times 10^{-1} = 6.667 \times 10^{-1} \\ d &= \frac{c}{7} = \frac{6.667 \times 10^{-1}}{7} = 9.524 \times 10^{-2} \end{aligned}\]

Markdown output

$$\begin{aligned} a &= 2 \\ b &= \frac{1}{3} = 0.33333 \end{aligned}$$

$$\begin{aligned} c &= a \cdot b = 2.000 \times 10^{0} \cdot 3.333 \times 10^{-1} = 6.667 \times 10^{-1} \\ d &= \frac{c}{7} = \frac{6.667 \times 10^{-1}}{7} = 9.524 \times 10^{-2} \end{aligned}$$

Every calculation in the session: the format_code option.

import handcalcs
handcalcs.set_option("format_code", ".3g")

Every session, permanently: set the option, then save it.

handcalcs.set_option("format_code", ".3g")
handcalcs.save_config()

In Jupyter there is also a line magic for the session setting:

%hc_format_code .3g

See Configuration for how saved options are stored and reset.

Values that are not plain numbers#

True and False are shown as words, not as 1 and 0.
Dates and times are shown in their usual str() form.
Collections (list, tuple, set, dict) format each element; long ones are shortened with an ellipsis.

ok = 3 > 2
today = datetime.date(2026, 10, 20)
xs = [1 / 3, 2 / 3, 1.0]           # hc: -f .2f
long_list = list(range(20))

Output (MarkdownRenderer)

Rendered

\[\begin{aligned} \mathrm{ok} &= 3 \gt 2 = \mathrm{True} \\ \mathrm{today} &= \mathrm{datetime}.\mathrm{date}\left(2026, 10, 20\right) = 2026-10-20 \\ \mathrm{xs} &= [0.33, 0.67, 1.00] \\ \mathrm{long}_{\mathrm{list}} &= \operatorname{list}\left(\operatorname{range}\left(20\right)\right) = [0, 1, 2, \ldots, 17, 18, 19] \end{aligned}\]

Markdown output

$$\begin{aligned} \mathrm{ok} &= 3 \gt 2 = \mathrm{True} \\ \mathrm{today} &= \mathrm{datetime}.\mathrm{date}\left(2026, 10, 20\right) = 2026-10-20 \\ \mathrm{xs} &= [0.33, 0.67, 1.00] \\ \mathrm{long}_{\mathrm{list}} &= \operatorname{list}\left(\operatorname{range}\left(20\right)\right) = [0, 1, 2, \ldots, 17, 18, 19] \end{aligned}$$

Any other object is formatted with the format code if it supports one (as forallpeople quantities do); otherwise its str() is shown. An object whose str() looks like <MyObject at 0x...> will be shown that way, so give your own classes a readable __str__ or __format__.

Next: Configuration.