questions of the century

0/index.md

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+# python prerequisites
+
+python is a programming language
+
+## jupyter support
+
+might convert py to ipynb later

0/tutorial.py

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+# pylint: disable=invalid-name # shut up ide
+"""
+python is a programming language
+
+and so it is very much like a programming language
+
+this file is going to show you how you will use a programming language
+"""
+
+# pylint: disable=pointless-string-statement
+"""
+python syntax is very uhh:
+it uses indentation instead of brackets {}, and no ;
+
+indentation:
+
+```python
+broski = "writing python in md in python"
+
+if len(broski) > 0:
+    print("inside a block")
+
+```
+
+normally you would see a lot of semicolons and brackets
+```rust
+let broski = "writing rust in here is crazy";
+
+if broski.len() > 0 {
+    println!("inside a block");
+}
+```
+
+but in python you just need to press enter.
+
+to get in a block you press four spaces more,
+and out of block you press four spaces less
+"""
+
+"""
+how to make a variable:
+name your variable name, place a single equal sign,
+then name your value
+"""  # remember a multiline string is not a comment
+
+my_var = 4
+
+# 4 is certainly a value of a type
+
+# pylint: disable=unidiomatic-typecheck
+assert type(my_var) == int  # yes use isinstance i know
+# oh yes two equal signs make a comparison between left and right
+# and return a boolean (true or false)
+"""
+assert will fail and crash if what after it is false:
+that means my var is an integer
+"""
+
+"you can change the content of the variable to whatever"
+# idk if it is a shadow (making past my_var out of use)
+# dont have to care tho
+my_var = 3.14
+# float has a dot in there. just put a dot in there
+
+
+assert type(my_var) == float  # pylint already disabled :)
+# still true; this file do not crash you can trust the assertions
+
+"there is a lot of types: float, int, bool also, and string:"
+
+my_var = "hello python"
+# its str now
+
+"""
+kinda lax isnt it. you can bind my_var to everything at this point.
+
+but not quite so lax: you can not just mention something you have not made
+"""
+
+try:  # this is a try block: errors/exceptions inside get captured...
+
+    # this is obviously an error
+    my_undeclared_var  # pyright: ignore reportUndefinedVariable # extension hell
+except NameError:  # ...in an except block, over here
+    print("my undeclared var is obviously undeclared")
+    # this will run will print to console
+# exceptions not captured will bubble
+
+"""
+certainly not so lax
+
+that is some values, we also have containers, which contain values
+"""
+
+my_list = [5, "list", "items", ("with", "different"), type]
+# type() is a function: you could put literally everthing
+
+"""
+values, including lists. yes, thats powering your 2d matrix.
+
+we have tuples, and set, and also dict. these are the python data types:
+"""
+
+my_tuple = ("these can not be changed", 2, 3.0)
+# tuple is just for grouping items to send somewhere together
+# if you want to change/add things you should be using any other types of container
+
+my_set = {
+    "unique",
+    "items",
+}
+
+my_dict = {
+    "key": "value",
+    # key must has __hash__ (for O(1) lookup)
+    # this is the existing my_var: see below
+    my_var: 12,
+    3 + 5: 8,
+}
+
+"""
+keys in dict and items in set have to be unique:
+school = {
+    "name": "mog school",
+    "class": "a",
+    "class": "b" # Not allowed
+}
+
+notice for dictionaries it goes like this:
+
+    key : value ,
+
+where key and value are both expressions.
+"""
+# but what are expressions?
+# they are the thing that can stay on right side of an assignment
+# variable = expression
+# lets consider this expression: my_var + " beginners"
+# it returns a value: "hello python beginners"
+# if whatever you do: putting down an existing variable, adding two variables,
+# calling a function, getting attributes...
+# returns values, then it must be an expression.
+# check wikipedia Python for more examples
+
+"""how do you aceess these containers?
+
+we have a sugar syntax: container[index]
+
+where index can be a value, in case of list and tuple:
+"""
+
+assert my_list[2] == "items"  # third item staring from 1,
+# so 2nd item starting from 0
+
+"index can be negative: different from C"
+
+assert my_tuple[-2] == 2
+
+"""for sets: good luck
+
+for dictionary you can use a value that is equal to
+an existing key:
+"""
+
+assert my_dict["hello python"] == 12
+
+"""
+for lists and tuples you would see a thing called a slice notation:
+
+start:end[:step]
+"""
+
+assert (my_list[2:5]) == ["items", ("with", "different"), type]
+
+"""
+start is inclusive, end is exclusive
+
+step makes it only index every (step) items from (start) and stop right before reaching (end)
+
+slice notation makes life easy
+"""
+
+assert (my_list[:5:2]) == [5, "items", type]
+
+"""use blank for start to denote first item,
+blank for end to denote past last item,
+and nothing for step means step by 1
+
+you may need this to select a range of items. its confusing but handy
+"""
+
+
+one_to_20 = list(range(1, 21))  # [1, ... , 20]
+weird_selection = [19, 15, 11, 7]
+
+assert one_to_20[-2:3:-4] == weird_selection
+# imagine instead of -2 its len(list) - 2. its handy for someone coming from C
+
+"""
+uh huh slice also takes negative number, and out of bounds number:
+one_to_20[30] would be index out of range, but
+one_to_20[20:30] simply returns empty array.
+"""
+
+"""we are here for math. calculations. functions.
+
+well:
+
+to define a function you go def my_function(my_param):
+then indent four spaces to get in the function block.
+"""
+
+
+def hello_world():
+    "print 'hello world' to console"
+    print("hello world")
+
+
+# as math person, there would be a lot of times where there are symbols and shit
+# naming it would be clear i would understand your code.
+# take some time. name your variable mu or theta or dvdt
+
+"""
+see that. indent. dedent. (outdent?)
+
+and you can define another function in in a function, unlike in c i would have to use closure [](){}
+
+for parameters you put in the () at the def over there. (a, b, c)
+and then in the fn body you would interact with them
+
+your function can return some values:
+"""
+
+
+# hey
+def quadratic_builder(a, b, c):
+    """this function returns a function with 1 parameter
+
+    calling the returned function with a number argument x would calculate
+
+    a * x ** 2 + b * x + c
+    """
+
+    def quadratic(x):
+        second_order = a * x**2
+        first_order = b * x
+        zeroth_order = c
+        # oh this looks redundant.
+        # but trust me when i say youll write code like this
+        return second_order + first_order + zeroth_order
+
+    return quadratic
+
+
+"""
+your function is already usable anywhere in the code
+
+to call any function you would do my_function()
+
+if the function needs params you supply it with arguments:
+"""
+
+x_minus_one_squared = quadratic_builder(1, -2, 1)
+
+assert x_minus_one_squared(3) == (3 - 1) ** 2 == 4
+
+"your function can have default params"
+
+
+def hello_to(name=None):
+    """if called with zero arguments, this function prints hello world
+
+    if supplied a name argument it will hello the name instead
+    """
+    if name is None:
+        print("hello world!")
+    else:
+        print(f"hello {name}!")
+
+
+"""
+in python you can pass in anything as a parameter.
+
+which is particularly scary, because i dont want to call 
+x_minus_one_squared("bad string") do i
+
+welcome to problem number one of python.
+
+Solution: type hints.
+"""
+# type hints are hints. which means you can still pass args with invalid types. coders be careful.
+
+
+def bungee_jumper(t: float, mass: float, drag_coeff: float) -> float:
+    """
+    using this funny ass function found in the slides:
+
+    v(t) = sqrt(g*m/cd) * tanh(sqrt(g*cd/m) * t)
+    """
+    # hey pylint this one im not sure
+    from math import sqrt, tanh  # pylint: disable=import-outside-toplevel
+
+    # manual check
+    if t < 0 or drag_coeff < 0 or mass <= 0:
+        raise ValueError("well uh its not possible is it")
+
+    # scipy where
+    g = 9.80665
+
+    if drag_coeff == 0 or t == 0:
+        return t * g  # please
+
+    term_vel = sqrt(g * mass / drag_coeff)
+    what_is_this = sqrt(g * drag_coeff / mass)
+
+    return term_vel * tanh(what_is_this * t)
+
+
+"""
+holy function
+
+with type hints over there you know what type of args you are supposed to put in and what would be returned, which is very handy.
+
+you can even put in default values!
+i love default values. there is some problems with certain types but i know to avoid it.
+
+that example is crazy
+"""
+
+"""
+truly math focused. Function first.
+
+we have conditionals and loops, which is a lot easier in code than in math:
+
+if, just like above.
+"""
+
+
+obvious = 1 + 1 == 2  # this operation returns true
+
+if obvious:
+    print("this will print")
+
+obviously_wrong = x_minus_one_squared(5) == 25
+
+if obviously_wrong:
+    print("you will never appear")
+else:
+    print("this will also print")
+
+
+"chaining if statements is easy with elif:"
+
+my_five = 5
+
+if 2 + 2 == my_five:
+    print("2 + 2 = 5")
+elif 2 + 3 == my_five:
+    print("2 + 3 = 5")
+elif 3 + 3 == my_five:
+    print("3 + 3 = 5")
+else:
+    print("D. None of the above")
+
+
+"""
+for.
+
+it is for element in collection. Remember: for element in collection.
+
+C for is ass: for (;;) which is ass.
+
+for of C is: 
+    for ([this statement runs once before the loop];
+        [this expressions is calculated if it returns 0 the loop stops];
+        [this statement runs after each loop])
+
+used a lot for running through an array:
+for (int i = 0; i < arr_size; i++);
+
+some wicked shit. notice that it is < and not <=. WHY do i have to care about that?
+NO you dont. 
+
+Python for is for element in iterable (which can be a collection, like an array)
+
+it is much easier to work with and much much less prone to bugs.
+
+yeah no segfaults for you here
+"""
+another_number = 1
+
+for number in one_to_20:
+    assert number == another_number
+    another_number += 1
+    # this would add 1 to itself
+
+# quick notice: this number variable can not be accessed outside the for loop.
+
+"""
+while.
+
+while condition is True:
+    # do something with the condition.        
+
+while just runs until the condition (after while before colon) is falsy.
+"""
+
+while another_number:
+    another_number -= 1
+
+assert another_number == 0
+
+"""
+sometimes you want to break out early:
+
+use break
+
+sometimes you want to skip some of the loops:
+
+use continue
+"""
+
+while True:
+    # if there is no break in this loop it would be BAD
+    another_number += 1
+    if another_number == 10:
+        # maybe the check is more sophisticated you cant put it in the while condition
+        # idfk your code your decision
+        break
+
+    if another_number in [4, 7]:
+        continue
+
+    print(another_number, "is not a bad number")  # this will skip 4 and 7
+
+# wtf
+
+
+"""
+errors. you get those when you use a thing and it doesnt run how you want, so it crashes and print:
+
+Traceback (most recent call last):
+  File "nmu/python/0/tutorial.py", line 442, in <module>
+    int("string")
+ValueError: invalid literal for int() with base 10: 'string'
+
+thats bad. someone raised an error on us.
+
+you can catch it with the try except block, and you can also raise your own error!
+
+previous examples have those. there are some common errors like TypeError or ValueError or IndexError etc. 
+how use? python docs got u. visit python docs
+"""
+
+"""
+custom model
+
+currently you are having a problem. you have a model of stuff, with this and that. 
+you have some things you want to get from the model.
+
+How would this work?
+"""