A calculator with automatic unit conversions
Project description
ucal
The ucal (unit calculator) module is a Pythonbased calculator which seamlessly integrates unit conversion.
Getting started
The ucal package requires Python 3.4+ to use. Install the package by running the following:
pip install user ucal
Once installed, the GUI can be run from the command line.
python m ucal_gui
In addition, ucal can be integrated into your own code as follows:
>>> import ucal
>>> ucal.interpret('5km in mi')
'3.10685596118667 mi'
>>> ucal.interpret('67 in hex')
'0x43'
>>> ucal.interpret('1m + 3ft')
'1.9144 m'
Screenshots
Method of operation
The uCal engine evaluates an expression using the folowing steps.
 Tokenizing
Tokenizing
Starting with a string expression, the string is broken up into substring, each of which represents a token. The following tokens are possible.

Value
 This is a number. Valid strings are
1
,1e67
,+1
,32.1E+526
, etc.
 This is a number. Valid strings are

Variable
 This is text such as
mm
,kg
, etc.
 This is text such as

Function
 A function follows the same rules as a variable, but is immediately followed by an opening parenthesis token.

Opening parenthesis
 This is the
(
sign.
 This is the

Closing parenthesis
 This is the
)
sign.
 This is the

Prefix operator

This operates on the value immediately following it, such as the first

in3  7
. 
Valid operators of this type are
+
and
.


Infix operator

An infix operator is an operator that operates on the value before and after it, such as
+
for addition. 
Valid operators of this type are
+
,
,*
,/
,^
for exponentiation, and%
for modulo operation.


Postfix operator

A postfix operator operates on the value immediately preceeding it.

The only valid operator of this type is the factorial operator
!
.

Interpret the percent sign
The percent sign %
can be either the modulo operator or a percentage. We interpret it by looking at its context and determining which makes sense.
It is interpreted as a percentage if the previous token is a value and either it is the last token in the expression, or the next token is an infix operator or an opening parenthesis.
Examples where it would be interpreted as the modulo operator are 1 % 2
.
Examples where it would be interpreted as a percentage are 30%
, and 80%  10%
.
Percentages are effectively replaced with *(0.01)
For example, 30%
becomes 30*(0.01)
.
Interpret implicit multiplication
Implicit multiplication is added between tokens as appropriate. There are a limited number of instances in which multiplication is implies. These are the following.

Between a value and a variable or function.
 Example:
1 in
is interpreted as1 * in
.
 Example:

Between a variable and a variable or function.
 Example:
in lbs
is interpreted asin * lbs
.
 Example:

Between a closing parenthesis and an opening parenthsis.
 Example:
(1) (2)
is interpreted as(1) * (2)
.
 Example:
Check syntax
The string of tokens is then checked for make sure the syntax makes sense.

Check for balanced parenthesis

Check prefix operators are followed by a quantity.

Check infix operators are preceeded and followed by a quantity.

Check postfix operators are preceeded by a quantity.

Check starting token is either a prefix operator or a quantity.

Check ending token is either a postfix operator or a quantity.
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