====== Computer Lab 06, modules, namespaces, conventions ======

Different **namespaces** in Python:
  * built-in namespace
  * global namespace
  * local namespace


**Python variable scope**: A scope is the portion of a program from where a namespace can be accessed directly without any prefix.

At any given moment, there are at least three nested scopes.

  * Scope of the current function which has local names
  * Scope of the module which has global names
  * Outermost scope which has built-in names
When a reference is made inside a function, the name is searched in the local namespace, then in the global namespace and finally in the built-in namespace.

<code python>
# Python program processing 
# global vs local variable
  
count = 5
def some_method(): 
    count = 10
    print(count) 
    return 

some_method() 
print(count)
</code>

<WRAP center round alert 60%>
<code python>
# local function shadowing a built-in one.
# REALLY BAD PRACTICE
# You should NEVER shadow a built-in function.

def abs(val):
    print("My abs() function")
    if  val >= 0:
        return val
    else:
        return -val


print(abs(-5))
</code>
</WRAP>

<fc #ff0000>PREFERRED SOLUTION: USE/WRITE YOUR OWN MODULE INSTEAD OF SHADOWING BUILT-IN FUNCTIONS!
</fc>
<WRAP group>
<WRAP half column>
//main.py//
<code python>
import mymath

print(abs(-4))
print(mymath.abs(-4))
</code>
</WRAP>

<WRAP half column>
//mymath.py//
<code python>
def abs(val):
    print("My abs() function")
    if  val >= 0:
        return val
    else:
        return -val

</code>
</WRAP>
</WRAP>

<WRAP center round box 80%>
===== Weekly homework 06 - trigonometric functions =====
  * Write a module ''mymath'' (file ''mymath.py'') with 2 functions:
<code python>
def cos(x):
    """Returns an approximate value of cos(x).
    :param x: float, input value for which the cosine function is computed
    :return: float, approximate value of cos(x)
    """

def sin(x):
    """Returns an approximate value of sin(x).
    :param x: float, input value for which the sine function is computed
    :return: float, approximate value of sin(x)
    """
</code> 
  * Use the following approximation of the sine and cosine function:
$\cos(x)=1-\frac{x^2}{2}+\frac{x^4}{24}$

$\sin(x)=x-\frac{x^3}{6}+\frac{x^5}{120}$

  * Create a file/module ''main.py'' and a function called ''get_trig_series(lst)'' inside it. Implement this function so that it receives a list of floats and outputs 2 lists - a list of approximate cosines of the values in the input list and a list of approximate sines of the values in the input list. Make use of the functions in the ''mymath'' module.

<code python>
    """Return lists of cosines and sines of the values in the input list 
    :param lst: list of floats, input values for this cos and sin functions are to be computed
    :return: list of floats, approximate cosines
    :return: list of floats, approximate sines

    Example:
    >>> cs, sn = get_trig_series([0, 0.1])
    >>> print(cs, sn)
    [1.0, 0.9950041666666667] [0.0, 0.09983341666666667]
    """
</code>

  * Pack both 'mymath.py' and 'main.py' in a single **zip file** and upload it to the BRUTE system. Place both files in the root directory of the zip file, that is, do NOT zip a folder containing the .py files. Zip them directly. 

</WRAP>

==== Built-in modules ====

<WRAP group>
<WRAP half column>
<code python>
import random

rng = random.Random()

# integer in range [1,6]
dice_throw = rng.randrange(1,7)

# odd integer in range [1, 199]
odd_number = rng.randrange(1,200,2)

# float drawn uniformy from a range [0, 1)
float_0_1 = rng.random()

# randomly shuffle list
shuffled_card_list = rng.shuffle(card_list)
</code>
</WRAP>

<WRAP half column>
<code python>
# Simulate throwing a dice 6000 times.
# Produce a list (of length 6) with frequency of each outcome (1-6).
</code>
</WRAP>
</WRAP>

<WRAP group>
<WRAP half column>
<code python>
import math

# constants
math.pi
math.e

# square root of 9
math.sqrt(9)

# degrees <-> radians conversion 
math.radians(90)
math.degrees(3.14)

# sin, cos, tan, ...
math.sin(math.radians(90))

# inverse trigonometric functions
math.asin(1.0)

# natural logarithm
math.log(math.e)

# base-10 logarithm
math.log10(1000)

</code>
</WRAP>

<WRAP half column>
  * **task 1:** Evaluate $f(x)= \sin(2x) \cos(2x) - \tan(x/2)$ for $x=45$ degrees.
  * **task 2:** Evaluate $\sqrt{x^2+y^2}$ for $x=2$, $y=100$. 
  * **task 3:** The radioisotope strontium-90 has a half-life of 38.1 years. A sample contains 100 mg of Sr-90. Calculate the remaining milligrams of Sr-90 after 100 years. $m(t)=m_o e^{- \ln(2)*t/T_{1/2}}$
</WRAP>
</WRAP>

===== homework =====
<note important>
Solve homework [[courses:be5b33prg:homework:regular:03_vector_library|03 - vectorlib - functions for working with vectors]] and submit it via Upload system in time! Check the deadline in Upload system.
</note>