I have an equation in the form of a string, something like this:
(20 + 3) / 4
I can easily solve this equation by using eval(), but it will give me an answer of 5, not the correct answer of 5.75. I know this is because 20, 3, and 4 are integers. So I was wondering, is there any way to just tack a .0 onto the end of them? Or is there some other trick I should use to make eval() think they are floats?
Note: the numbers will not always be integers, so it would be great if the solution could detect if they are integers and treat them accordingly.
Note #2: I'm using python 2.7
Note #3: I already know that "Python 2 is legacy, Python 3 is the future."
Thanks!
You could use sympy to parse the string using sympy_parser.parse_expr and then solve/simplify it:
>>> from sympy.parsing import sympy_parser
>>> exp = '(20 + 3) / 4'
>>> sympy_parser.parse_expr(exp).round(2)
5.75
This would also work for other valid mathematical expressions.
Related
This question already has answers here:
Dynamically calculated zero padding in format string in python
(2 answers)
How do I pad a string with zeroes?
(19 answers)
Closed 9 months ago.
Sorry if this is a bit of a noob question. But moving on..
Say at the beginning of my code I set a variable, like this:
TestVar = 'A6'
But I later want it to print out as 000000A6
Or say it was
TestVar = 'C30'
I'd want it to print out as 00000C30
Basically always returning it with a length of 8
The reasoning for this is I've made a general script for modding a game, (I can link if asked) and you need to put in certain values which I want to have format automatically for ease of use. For example on running it'll print
Item ID Here:
And if you put in 166 it would convert the decimal number to hex which would be A6, however in order to be usable for all values (not just ones that are 2 digits once converted) I'm trying to make it detect it's length and format it with the 0s before.
Sorry if this doesnt make sense, in a simpler way of saying this, is there a way for it to detect the length of a variable? So for example in pseudo
TestVar = 'C30'
If TestVar length = 3
print('00000'+TestVar)
Print Result: 00000C30
Basically always returning it with a length of 8
That's what format strings do:
>>> print(f"{'C30':>08s}")
00000C30
As a sidenote, to output any number as 8-digit hex:
>>> print(f"{100:>08X}")
00000064
>>> print(f"{1024:>08X}")
00000400
See the documentation:
for f-strings (the f'I am an f-string' syntax);
for formatting syntax (the >08s and >08X thing).
Use string function rjust():
print(test.rjust(8,'0'))
The .zfill string method can be used.
For example:
s = 'C30'
s.zfill(8)
>>> '00000C30'
Try this code
txt = "A6"
x = txt.zfill(8)
print(x)
You can use string.zfill method
for example.
code = '3C0'
filledCode = code.zfill(8)
this method filled with zero the number of digit that you pass like a parameter
try something like this str.rjust() function
i = 1111
pad = '0'
n = 8
x = str(i).rjust(n, pad)
print(x) # 00001111
I have a function taking float arguments (generally integers or decimals with one significant digit), and I need to output the values in a string with two decimal places (5 → 5.00, 5.5 → 5.50, etc). How can I do this in Python?
Since this post might be here for a while, lets also point out python 3 syntax:
"{:.2f}".format(5)
You could use the string formatting operator for that:
>>> '%.2f' % 1.234
'1.23'
>>> '%.2f' % 5.0
'5.00'
The result of the operator is a string, so you can store it in a variable, print etc.
f-string formatting:
This was new in Python 3.6 - the string is placed in quotation marks as usual, prepended with f'... in the same way you would r'... for a raw string. Then you place whatever you want to put within your string, variables, numbers, inside braces f'some string text with a {variable} or {number} within that text' - and Python evaluates as with previous string formatting methods, except that this method is much more readable.
>>> foobar = 3.141592
>>> print(f'My number is {foobar:.2f} - look at the nice rounding!')
My number is 3.14 - look at the nice rounding!
You can see in this example we format with decimal places in similar fashion to previous string formatting methods.
NB foobar can be an number, variable, or even an expression eg f'{3*my_func(3.14):02f}'.
Going forward, with new code I prefer f-strings over common %s or str.format() methods as f-strings can be far more readable, and are often much faster.
String Formatting:
a = 6.789809823
print('%.2f' %a)
OR
print ("{0:.2f}".format(a))
Round Function can be used:
print(round(a, 2))
Good thing about round() is that, we can store this result to another variable, and then use it for other purposes.
b = round(a, 2)
print(b)
Use round() - mostly for display purpose.
String formatting:
print "%.2f" % 5
If you actually want to change the number itself instead of only displaying it differently use format()
Format it to 2 decimal places:
format(value, '.2f')
example:
>>> format(5.00000, '.2f')
'5.00'
Using python string formatting.
>>> "%0.2f" % 3
'3.00'
Shortest Python 3 syntax:
n = 5
print(f'{n:.2f}')
In Python 3
print(f"{number:.2f}")
A shorter way to do format.
I know it is an old question, but I was struggling finding the answer myself. Here is what I have come up with:
Python 3:
>>> num_dict = {'num': 0.123, 'num2': 0.127}
>>> "{0[num]:.2f}_{0[num2]:.2f}".format(num_dict)
0.12_0.13
I faced this problem after some accumulations. So What I learnt was to multiply the number u want and in the end divide it to the same number. so it would be something like this: (100(x+y))/100 = x+y if ur numbers are like 0.01, 20.1, 3,05.
You can use number * (len(number)-1)**10 if your numbers are in unknown variety.
If you want to get a floating point value with two decimal places limited at the time of calling input,
Check this out ~
a = eval(format(float(input()), '.2f')) # if u feed 3.1415 for 'a'.
print(a) # output 3.14 will be printed.
Using Python 3 syntax:
print('%.2f' % number)
This question already has answers here:
Evaluating a mathematical expression in a string
(14 answers)
Closed 3 years ago.
Is there a way to solve math equations that are in string format?
For example, I have
x = 2
y = 3
equations_str = ('x+y', 'x-y')
and I want a function that will give
results = (5, -1)
I want to do this because I want to have the equations as titles of figures, so they need to be strings.
I'm aware that a similar question was asked for java, but I'm not familiar enough with java so translate it to python.
Thanks!
Look into eval() https://www.geeksforgeeks.org/eval-in-python/ You can write statements and execute them.
eval example (interactive shell):
>>> x = 1
>>> eval('x + 1')
2
>>> eval('x')
1
As Jam mentioned, you can do the following:
equations_str = (eval('x+y'), eval('x-y'))
The only way I can think of solving this problem is to take your equation, calculate it as a regular integer, and then convert it into a string using str(). Then you could put that result into an array before proceeding. The only thing is that this method won't work for large amounts, but if you only need a few, this should work. Hope this helps, Luke.
Try the sympify function of the sympy package. It lets you evaluate strings, but uses the eval function, so do not use it on unsanitized input.
Example:
>>> from sympy import sympify
>>> str_expr = "x**2 + 3*x - 1/2"
>>> expr = sympify(str_expr)
>>> expr
x**2 + 3*x - 1/2
>>> expr.subs(x, 2)
19/2
This question already has answers here:
Python int to binary string?
(36 answers)
Closed 6 years ago.
When converting a number in binary in Python what you get is the following:
b = bin(77)
print(b) # 0b1001101
When I was expecting 01001101. I am guessing that the b is there to let Python know that this is a binary number and not some integer. And that is ok within Python but what is considered safe practise here if you want to communicate with the outside world? This might be a silly example but online converters for instance do not recognise the above binary.
Would simply removing b always do the trick? Because I seem to be running into problems trying to code the Ascii85 encoder/decoder where concatenations of binary numbers take place. You can take a look at this example here.
My code is this case produces the following:
ch = 'Man '
list_ = [ord(x) for x in ch] # [77, 97, 110, 32]
binary_repr = ''.join(bin(x) for x in list_) # 0b10011010b11000010b11011100b100000
# When it should be 01001101011000010110111000100000
Notice that simply replacing the b with nothing doesn't quite cut it here. This is probably some dumm mistake but can someone clear things up for me?
>>> format(b, '08b')
Where b is your number and '08b' is the number of bit you want to use representing your number, if the parameter is #08b instead of 08b, you get the 0b in front of the number.
use format in every further operation and you should be good!
Doesn't
str(b)[2:]
do the job?
But you'll maybe better do:
"{0:b}".format(77)
Is it possible in Python to calculate a term in a string?
For example:
string_a = "4 ** (3 - 2)"
unknown_function(string_a) = 4
Is this possible? Is there a function that mimics "unknown_function" in my example?
Just like sympy was a useful module for your last question, it can apply here:
>>> import sympy
>>> sympy.sympify("4**(3-2)")
4
and even
>>> sympy.sympify("2*x+y")
2*x + y
>>> sympy.sympify("2*x+y").subs(dict(x=2, y=3))
7
Note though that this will return sympy objects, and if you want to get an integer or a float out of it you should do the conversion explicitly:
>>> type(sympy.sympify("4**(3-2)"))
<class 'sympy.core.numbers.Integer'>
>>> int(sympy.sympify("4**(3-2)"))
4
I hacked together a recipe to turn string expressions into functions here which is kind of cute.
There is eval
eval(string_a)
# 4
But do not use this under any circumstances if string_a comes from anyone but you, because they can easily hack into your system and destroy your files!
Yes, you can use the eval function.
>>> string_a = "4 ** (3 - 2)"
>>> eval(string_a)
4
>>>
You can read more in the documentation
There is a module py-expression-eval, that does not depend on the use of eval. It can be used to evaluate strings as a mathematical expression, even symbolic expressions can be evaluated.
from py_expression_eval import Parser
parser = Parser()
expr = parser.parse("4 ^ (3 - 2)")
expr.evaluate({})
For the use with symbolic expressions see:https://axiacore.com/blog/mathematical-expression-evaluator-python/