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Can MathJax use anything else than curly braces to write symbols like sqrt{} or frac{}?

I'm using MathJax to render math equations on my website. I use Python to create those math equations and I use f-strings a lot.
Currently, I have to concatenate every string because to write a square root in mathJax (as far as I can tell), you can only use sqrt{x=3}, but that's a problem because in Python f-strings use {} too.
Is there any other way to write a square root in mathJax or fraction in mathJax without using curly brackets?
An example of what I'm talking about/in other words:
Off of what I know currently, this is how you write a square root in mathJax:
$$sqrt{4}$$
But in Python when dealing with f-strings:
x = 4
equation = f'$$sqrt{x}$$'
creates
$$sqrt4$$
– which is not what I want.
Of course I see that you can just concatenate the string by doing and not do an f-string:
equation = '$$sqrt{' + x + '}$$'
However when I'm doing larger problems, and I'm making a lot of varying equations and this takes forever to do for every string.

Solve single variable equation using if, else and while statements in python

I am tutoring a 7th grade student in basic programming and mathematics. One of the problems the students needs to complete for a class assignment is "create a program to solve a given single variable linear equation". The student is required to use python and only use if, else and while statements. The program can include user defined functions and lists but cannot import any libraries like regex, sympy, numpy, etc.
The program should be able to solve these example equations:
2*x - 5 = 8
4*x + 3 = 3*x - 10
11*x = 2 - (1/5)*x
4*(x + 2) = 5*(x + 9)
I tried: For each character in the string note the numerals, operators, equals to sign and variable. Copy the variable and its coefficient into a new string and the constants with their signs to another string. My hope was that I would eventually extract the integers from each string and solve the equation for x. But I wasn't correctly capturing numbers with multiple digits. And the equation with parentheses completely stumped me. Not being able to use regex or sympy is painful!
I am looking for a pythonic solution to this problem if it exists.
I feel this is a very difficult question for a 7th grader because my grad and undergrad friends haven't been able to come up with a solution. Any advice on how to proceed will help if a programmatic solution isn't available.
Thank you.

Although it is completely possible to build a finite automaton solve an expression, it is not an easy task.
I myself had lots of assignments related to build a semantic or syntax parser, but it is usually done in C: https://codereview.stackexchange.com/questions/112620/simple-expression-calculator-in-c.
Nonetheless, if you accept a clever/dangerous/bad-practice solution:
def solve_expression(expr, var="x"):
expr = expr.replace(var, "1j")
left, right = map(eval, expr.split("="))
return (right.real-left.real)/(left.imag-right.imag)
print(solve_expression("2*x - 5 = 8"))
print(solve_expression("4*x + 3 = 3*x - 10"))
print(solve_expression("11*x = 2 - (1/5)*x"))
print(solve_expression("4*(x + 2) = 5*(x + 9)"))
The idea is to convert the free variable to the imaginary unit and let python interpreter do the rest.

Python - calculator program and strings

I am new to Python and am trying to write a calculator program. I have been trying to do the following but with no success, so please point me in the right direction:
I would like to input an equation as a user, for example:
f(t) = 2x^5 + 8
the program should recognize the different parts of a string and in this case make a variable f(t) and assign 2x^5 + 8 to it.
Though, if I input an equation followed by an equals sign, for example
2x^5 + 8 =
the program will instead just output the answer.
I am not asking how to code for the math-logic of solving the equation, just how to get the program to recognize the different parts of a string and make decisions accordingly.
I am sorry I don't have any code to show as an attempt as I'm not sure how to go about this and am looking for a bit of help to get started.
Thank you.

For a little bit of context: The problem you're describing is more generally known as parsing, and it can get rather complicated, depending on the grammar. The grammar is the description of the language; the language, in your case, is the set of all valid formulas for your calculator.
The first recommended step, even before you start coding, is to formalize your grammar. This is mainly for your own benefit, as it will make the programming easier. A well established way to do this is to describe the grammar using EBNF, and there exist tools like PLY for Python that you can use to generate parsers for such languages.
Let's try a simplified version of your calculator grammar:
digit := "0" | "1" # our numbers are in binary
number := digit | number digit # these numbers are all nonnegative
variable := "x" | "y" # we recognize two variable names
operator := "+" | "-" # we could have more operators
expression := number | variable | "(" expression operator expression ")"
definition := variable "=" expression
evaluation := expression "="
Note that there are multiple problems with this grammar. For example:
What about whitespace?
What about negative numbers?
What do you do about inputs like x = x (this is a valid definition)?
The first two are probably problems with the grammar itself, while the last one might need to be handled at a later stage (is the language perhaps context sensitive?).
But anyway, given such a grammar a tool like PLY can generate a parser for you, but leaving it up to you to handle any additional logic (like x = x). First, however, I'd suggest you try to implement it on your own. One idea is to write a so called Top Down Parser using recursion.

Python- stuck trying to create a "free hand" calculator

I'm trying to create a calculator program in which the user can type an equation and get an answer. I don't want the full code for this, I just need help with a specific part.
The approach I am trying to take is to have the user input the equation as a string (raw_input) and then I am trying to convert the numbers from their input to integers. After that I need to know how I can get the operands to do what I want them to do depending on which operand the user uses and where it is in the equation.
What are some methods I might use to accomplish this task?
Here is basically what I have right now:
equation_number = raw_input("\nEnter your equation now: ")
[int(d) for d in equation_number if d.isdigit()]
Those lines are just for collecting input and attempting to convert the numbers into integers. Unfortunately, it does not seem to be working very well and .isdigit will only work for positive numbers anyway.
Edit- aong152 mentioned recursive parsing, which I looked into, and it appears to have desirable results:
http://blog.erezsh.com/how-to-write-a-calculator-in-70-python-lines-by-writing-a-recursive-descent-parser/
However, I do not understand the code that the author of this post is using, could anyone familiarize me with the basics of recursive parsing?

The type of program you are trying to make is probably more complicated than you think
The first step would be separating the string into each argument.
Let's say that the user inputs:
1+2.0+3+4
Before you can even convert to ints, you are going to need to split the string up into its components:
1
+
2.0
+
3
+
4
This will require a recursive parser, which (seeing as you are new to python) maybe be a bit of a hurdle.
Assuming that you now have each part seperately as strings,
float("2.0") = 2.0
int(2.0) = 2
Here is a helper function
def num (s):
try:
return int(s)
except exceptions.ValueError:
return int(float(s))

instead of raw_input just use input because raw_input returns a string and input returns ints
This is a very simple calculator:
def calculate():
x = input("Equation: ")
print x
while True:
calculate()
the function takes the input and prints it then the while loop executes it again
im not sure if this is what you want but here you go and also you should make a way to end the loop

After using raw_input() you can use eval() on the result to compute the value of this string. eval() evaluates any valid Python expression and returns the outcome.
But I think this is not to your liking. You probably want to do more by yourself.
So I think you should have a look at the re module to split the input using regular expressions into tokens (sth like numbers and operators). After this you should write a parser which gets the token stream as input. You should decide whether this parser shall just return the computed value (e. g. a number) or maybe an abstract syntax tree, i. e. a data structure which represents the expression in an object-oriented (instead of character-oriented) way. Such an Absy could then be evaluated to get the final result.

Are you familiar with regular expressions? If not, it's probably a good idea to first learn about them. They are the weak, non-recursive cousin of parsing. Don't go deep, just understand the building blocks — A then B, A many times, A or B.
The blog post you found is hard because it implements the parsing by hand. It's using recursive descent, which is the only way to write a parser by hand and keep your sanity, but it's still tricky.
What people do most of the time is only write a high level grammar and use a library (or code generator) to do the hard work of parsing.
Indeed he had an earlier post where he uses a library:
http://blog.erezsh.com/how-to-write-a-calculator-in-50-python-lines-without-eval/
At least the beginning should be very easy. Things to pay attention to:
How precedence arises from the structure of the grammar — add consists of muls, not vice versa.
The moment he adds a rule for parentheses:
atom: neg | number | '(' add ')';
This is where it really becomes recursive!
6-2-1 should parse as (6-2)-1, not 6-(2-1). He doesn't discuss it, but if you look
carefully, it also arises from the structure of the grammar. Don't waste tome on this; just know for future reference that this is called associativity.
The result of parsing is a tree. You can then compute its value in a bottom-up manner.
In the "Calculating!" chapter he does that, but the in a sort of magic way.
Don't worry about that.
To build a calculator yourself, I suggest you strip the problem as much as possible.
Recognizing where numbers end etc. is a bit messy. It could be part of the grammar, or done by a separate pass called lexer or tokenizer.
I suggest you skip it — require the user to type spaces around all operators and parens. Or just assume you're already given a list of the form [2.0, "*", "(", 3.0, "+", -1.0, ")"].
Start with a trivial parser(tokens) function that only handles 3-element expressions — [number, op, number].
Return a single number, the result of the computation. (I previously said parsers output a tree which is processed later. Don't worry about that, returning a number is simpler.)
Write a function that expects either a number or parentheses — in the later case it calls parser().
>>> number_or_expr([1.0, "rest..."])
(1.0, ["rest..."])
>>> number_or_expr(["(", 2.0, "+", 2.0, ")", "rest..."])
(4.0, ["rest..."])
Note that I'm now returning a second value - the remaining part of the input. Change parser() to also use this convention.
Now Rewrite parser() to call number_or_expr() instead of directly assuming tokens[0] and tokens[2] are numbers.
Viola! You now have a (mutually) recursive calculator that can compute anything — it just has to be written in verbose style with parens around everything.
Now stop and admire your code, for at least a day :-) It's still simple but has the essential recursive nature of parsing. And the code structure reflects the grammar 1:1 (which is the nice property of recursive descent. You don't want to know how the other algorithms look).
From here there many improvements possible — support 2+2+2, allow (1), precedence... — but there are 2 ways to go about it:
Improve your code step by step. You'll have to refactor a lot.
Stop working hard and use a parsing library, e.g. pyparsing.
This will allow you to experiment with grammar changes faster.

Why allow concatenation of string literals?

I was recently bitten by a subtle bug.
char ** int2str = {
"zero", // 0
"one", // 1
"two" // 2
"three",// 3
nullptr };
assert( int2str[1] == std::string("one") ); // passes
assert( int2str[2] == std::string("two") ); // fails
If you have godlike code review powers you'll notice I forgot the , after "two".
After the considerable effort to find that bug I've got to ask why would anyone ever want this behavior?
I can see how this might be useful for macro magic, but then why is this a "feature" in a modern language like python?
Have you ever used string literal concatenation in production code?

Sure, it's the easy way to make your code look good:
char *someGlobalString = "very long "
"so broken "
"onto multiple "
"lines";
The best reason, though, is for weird printf formats, like type forcing:
uint64_t num = 5;
printf("Here is a number: %"PRIX64", what do you think of that?", num);
There are a bunch of those defined, and they can come in handy if you have type size requirements. Check them all out at this link. A few examples:
PRIo8 PRIoLEAST16 PRIoFAST32 PRIoMAX PRIoPTR

It's a great feature that allows you to combine preprocessor strings with your strings.
// Here we define the correct printf modifier for time_t
#ifdef TIME_T_LONG
#define TIME_T_MOD "l"
#elif defined(TIME_T_LONG_LONG)
#define TIME_T_MOD "ll"
#else
#define TIME_T_MOD ""
#endif
// And he we merge the modifier into the rest of our format string
printf("time is %" TIME_T_MOD "u\n", time(0));

I see several C and C++ answers but none of the really answer why or really what was the rationale for this feature? In C++ this is feature comes from C99 and we can find the rationale for this feature by going to Rationale for International Standard—Programming Languages—C section 6.4.5 String literals which says (emphasis mine):
A string can be continued across multiple lines by using the backslash–newline line continuation, but this requires that the continuation of the string start in the first position of the next line. To permit more flexible layout, and to solve some preprocessing problems (see §6.10.3), the C89 Committee introduced string literal concatenation. Two string literals in a row are pasted together, with no null character in the middle, to make one combined string literal. This addition to the C language allows a programmer to extend a string literal beyond the end of a physical line without having to use the backslash–newline mechanism and thereby destroying the indentation scheme of the program. An explicit concatenation operator was not introduced because the concatenation is a lexical construct rather than a run-time operation.
Python which seems to have the same reason, this reduces the need for ugly \ to continue long string literals. Which is covered in section 2.4.2 String literal concatenation of the
The Python Language Reference.

Cases where this can be useful:
Generating strings including components defined by the preprocessor (this is perhaps the largest use case in C, and it's one I see very, very frequently).
Splitting string constants over multiple lines
To provide a more concrete example for the former:
// in version.h
#define MYPROG_NAME "FOO"
#define MYPROG_VERSION "0.1.2"
// in main.c
puts("Welcome to " MYPROG_NAME " version " MYPROG_VERSION ".");

I'm not sure about other programming languages, but for example C# doesn't allow you to do this (and I think this is a good thing). As far as I can tell, most of the examples that show why this is useful in C++ would still work if you could use some special operator for string concatenation:
string someGlobalString = "very long " +
"so broken " +
"onto multiple " +
"lines";
This may not be as comfortable, but it is certainly safer. In your motivating example, the code would be invalid unless you added either , to separate elements or + to concatenate strings...

From the python lexical analysis reference, section 2.4.2:
This feature can be used to reduce the
number of backslashes needed, to split
long strings conveniently across long
lines, or even to add comments to
parts of strings
http://docs.python.org/reference/lexical_analysis.html

For rationale, expanding and simplifying Shafik Yaghmour’s answer: string literal concatenation originated in C (hence inherited by C++), as did the term, for two reasons (references are from Rationale for the ANSI C Programming Language):
For formatting: to allow long string literals to span multiple lines with proper indentation – in contrast to line continuation, which destroys the indentation scheme (3.1.4 String literals); and
For macro magic: to allow the construction of string literals by macros (via stringizing) (3.8.3.2 The # operator).
It is included in the modern languages Python and D because they copied it from C, though in both of these it has been proposed for deprecation, as it is bug-prone (as you note) and unnecessary (since one can just have a concatenation operator and constant folding for compile-time evaluation; you can’t do this in C because strings are pointers, and so you can’t add them).
It’s not simple to remove because that breaks compatibility, and you have to be careful about precedence (implicit concatenation happens during lexing, prior to operators, but replacing this with an operator means you need to be careful about precedence), hence why it’s still present.
Yes, it is in used production code. Google Python Style Guide: Line length specifies:
When a literal string won't fit on a single line, use parentheses for implicit line joining.
x = ('This will build a very long long '
'long long long long long long string')
See “String literal concatenation” at Wikipedia for more details and references.

So that you can split long string literals across lines.
And yes, I've seen it in production code.

While people have taken the words out of my mouth about the practical uses of the feature, nobody has so far tried to defend the choice of syntax.
For all I know, the typo that can slip through as a result was probably just overlooked. After all, it seems robustness against typos wasn't at the front of Dennis's mind, as shown further by:
if (a = b);
{
printf("%d", a);
}
Furthermore, there's the possible view that it wasn't worth using up an extra symbol for concatenation of string literals - after all, there isn't much else that can be done with two of them, and having a symbol there might create temptation to try to use it for runtime string concatenation, which is above the level of C's built-in features.
Some modern, higher-level languages based on C syntax have discarded this notation presumably because it is typo-prone. But these languages have an operator for string concatenation, such as + (JS, C#), . (Perl, PHP), ~ (D, though this has also kept C's juxtaposition syntax), and constant folding (in compiled languages, anyway) means that there is no runtime performance overhead.

Another sneaky error I've seen in the wild is people presuming that two single quotes are a way to escape the quote (as it is commonly used for double quotes in CSV files, for example), so they'll write things like the following in python:
print('Beggars can''t be choosers')
which outputs Beggars cant be choosers instead of the Beggars can't be choosers the coder desired.
As for the original "why" question: why is this a "feature" in a modern language like python? - in my opinion, I concur with the OP, it shouldn't be.