Python basics and environment setup

name = "Aylin"
age = 20
height = 1.75
is_student = True

print(name)
print(age)
print(height)
print(is_student)

name = "Aylin"
age = 20

print("Name:", name)            # several values, separated by a space
print("Age:", age)
print("Data", "Science", sep="-")  # choose the separator
print("Same", end=" ")           # do not jump to a new line
print("line")

# This whole line is a comment. Python skips it.
price = 100   # A comment can also follow code on the same line.
# print(price * 2)   <- this line is "commented out", so it does not run
print(price)

age = 20
age = 21        # the box now holds 21
age = age + 1   # take the old value, add 1, store it back
print(age)

a, b, c = 1, 2, 3     # three boxes in one line
print(a, b, c)

x = y = 0             # the same value into two boxes
print(x, y)

first = "tea"
second = "coffee"
first, second = second, first   # swap the two values
print(first, second)

age = 20
Age = 30
AGE = 40
print(age, Age, AGE)   # three different variables

x = 5
print(type(x))
x = "five"          # the same name now holds text
print(type(x))

print(type(20))
print(type(3.5))
print(type("hello"))
print(type(True))
print(type(None))

age = 20
print(isinstance(age, int))    # is age an int?
print(isinstance(age, str))    # is age a str?

print(3 + 2)         # int + int gives int
print(3 + 2.0)       # int + float gives float
print(10 / 5)        # / always gives float
print(type(3 + 2.0))

print(abs(-7))             # distance from zero
print(round(3.14159, 2))   # round to 2 decimals
print(round(7.6))          # round to a whole number
print(min(4, 9, 1))        # smallest
print(max(4, 9, 1))        # largest
print(pow(2, 5))           # same as 2 ** 5
print(divmod(17, 5))       # (17 // 5, 17 % 5)

print(round(2.5))   # rounds to the nearest EVEN number
print(round(3.5))
print(round(4.5))

population = 8_100_000_000   # underscores make long numbers readable
print(population)

distance = 1.5e3             # scientific notation: 1.5 x 10 to the power 3
print(distance)
tiny = 2e-4                  # 2 x 10 to the power -4
print(tiny)

print(2 ** 100)   # Python integers have no size limit

print(0.1 + 0.2)
print(0.1 + 0.2 == 0.3)
print(round(0.1 + 0.2, 2))

single = 'Hello'
double = "Hello"
with_apostrophe = "It's Python"
many_lines = """Line one
Line two"""

print(single, double)
print(with_apostrophe)
print(many_lines)

print("Name:\tAylin")             # \t is a tab
print("First line\nSecond line")  # \n starts a new line
print("She said \"hi\"")          # \" puts a quote inside quotes
print("C:\\Users\\aylin")         # \\ is one backslash

word = "Python"
print(word[0])     # first character
print(word[5])     # sixth character
print(word[-1])    # last character
print(word[-2])    # second from the end
print(len(word))   # number of characters

word = "Python"
print(word[0:3])   # from 0 up to (not including) 3
print(word[2:])    # from 2 to the end
print(word[:4])    # from the start up to 4
print(word[-3:])   # the last three
print(word[::2])   # every second character
print(word[::-1])  # reversed

first = "Data"
second = "Science"
print(first + " " + second)   # join with +
print("ha" * 3)               # repeat with *
print("-" * 20)               # a quick divider line

text = "python for Data Science"
print(text.upper())
print(text.lower())
print(text.title())
print(text.capitalize())
print(text.swapcase())

raw = "   Aylin   "
print("[" + raw + "]")
print("[" + raw.strip() + "]")    # both sides
print("[" + raw.lstrip() + "]")   # left side only
print("[" + raw.rstrip() + "]")   # right side only

sentence = "I like cats. Cats are great."
print(sentence.replace("cats", "dogs"))   # case-sensitive: "Cats" stays
print(sentence.replace("a", "@", 2))      # only the first 2 matches

csv_line = "apple,banana,cherry"
fruits = csv_line.split(",")       # text -> list
print(fruits)
print(" | ".join(fruits))          # list -> text

words = "Data science is fun".split()   # split on spaces
print(words)
print(len(words))

text = "banana"
print(text.find("an"))         # position of the first match
print(text.find("x"))          # -1 means "not found"
print(text.index("n"))         # like find, but an error if missing
print(text.count("a"))         # how many times
print(text.startswith("ban"))
print(text.endswith("na"))
print("nan" in text)

print("2026".isdigit())     # only digits?
print("Aylin".isalpha())    # only letters?
print("abc123".isalnum())   # letters or digits?
print("   ".isspace())      # only spaces?
print("HELLO".isupper())
print("hello".islower())

name = "Aylin"
score = 87.456
students = 1250

print(f"{name} scored {score} points")
print(f"Rounded: {score:.1f}")            # 1 decimal place
print(f"Two decimals: {score:.2f}")
print(f"Total students: {students:,}")    # thousands separator
print(f"Next year: {20 + 1}")             # any expression works

word = "Python"
word[0] = "J"

word = "Python"
new_word = "J" + word[1:]   # build a new string instead
print(new_word)
print(word)                 # the original is unchanged

is_raining = True
print(is_raining)
print(type(is_raining))
print(5 > 3)       # comparisons give booleans
print(10 == 9)

print(True + True)   # True counts as 1
print(int(False))    # False counts as 0

print(bool(0), bool(42), bool(-1))
print(bool(""), bool("hi"), bool(" "))
print(bool([]), bool([0]))
print(bool(None))

result = None
print(result)
print(type(result))
print(result is None)

answer = print("Hello")   # print shows text but gives back nothing
print(answer)

fruits = ["apple", "banana", "cherry"]
print(fruits[0])          # apple  (counting starts at 0!)
fruits.append("mango")    # adds an item to the end
print(len(fruits))        # 4

student = {"name": "Aylin", "age": 20}
print(student["name"])    # Aylin

print({1, 2, 2, 3})       # {1, 2, 3}  (duplicates removed)

fruits = ["apple", "banana", "cherry"]
numbers = [4, 8, 15, 16, 23, 42]
mixed = ["Aylin", 20, 1.75, True]   # different types are allowed
empty = []

print(fruits)
print(len(numbers))
print(mixed)
print(empty)

fruits = ["apple", "banana", "cherry", "mango"]
print(fruits[0])     # first
print(fruits[-1])    # last
print(fruits[1:3])   # slice: positions 1 and 2
print(fruits[:2])    # the first two

fruits = ["apple", "banana", "cherry"]
fruits[1] = "blueberry"   # lists can change
print(fruits)

fruits = ["apple", "banana"]
fruits.append("cherry")          # add to the end
fruits.insert(0, "mango")        # add at position 0
fruits.extend(["kiwi", "lime"])  # add several
print(fruits)

fruits = ["apple", "banana", "cherry", "banana", "kiwi"]
fruits.remove("banana")    # removes the FIRST match
print(fruits)

last = fruits.pop()        # removes and gives back the last item
print(last, fruits)

second = fruits.pop(1)     # removes and gives back position 1
print(second, fruits)

del fruits[0]              # deletes position 0
print(fruits)

nums = [3, 7, 3, 9, 3]
print(7 in nums)        # is it in the list?
print(nums.index(9))    # where is it?
print(nums.count(3))    # how many times?

scores = [72, 95, 58, 88]
print(sorted(scores))     # a NEW sorted list
print(scores)             # the original is unchanged

scores.sort()             # sorts the list itself
print(scores)
scores.sort(reverse=True) # largest first
print(scores)
scores.reverse()          # flip the current order
print(scores)

scores = [72, 95, 58, 88]
print(len(scores))
print(min(scores), max(scores))
print(sum(scores))
print(sum(scores) / len(scores))   # the average

print([1, 2] + [3, 4])   # join two lists
print([0] * 5)           # repeat a list

grid = [[1, 2, 3],
        [4, 5, 6]]
print(grid[1])      # the second row
print(grid[1][2])   # row 1, position 2

a = [1, 2, 3]
b = a            # b is the SAME list, not a copy
b.append(4)
print(a)         # a changed too!

c = a.copy()     # a real copy
c.append(5)
print(a)
print(c)

print(list(range(5)))          # 0 up to 5 (not including 5)
print(list(range(2, 10, 2)))   # start 2, stop 10, step 2

point = (3, 4)
colors = ("red", "green", "blue")
single = (5,)        # one item needs a comma
not_a_tuple = (5)    # just the number 5 in brackets

print(point, colors)
print(type(single))
print(type(not_a_tuple))

colors = ("red", "green", "blue", "green")
print(colors[0])
print(colors[-1])
print(colors[1:3])
print(len(colors))
print(colors.count("green"))
print(colors.index("blue"))

point = (3, 4)
x, y = point        # unpacking: one value per name
print(x)
print(y)

colors = ("red", "green", "blue")
colors[0] = "pink"

print((1, 2) + (3,))
print(("ha",) * 3)

student = {"name": "Aylin", "age": 20, "course": "Data Science"}
print(student)
print(len(student))   # number of key-value pairs

student = {"name": "Aylin", "age": 20}
print(student["name"])                 # by key
print(student.get("age"))              # same, but safe
print(student.get("email"))            # missing key -> None
print(student.get("email", "not given"))   # missing key -> your default

student = {"name": "Aylin", "age": 20}
print(student["email"])

student = {"name": "Aylin", "age": 20}
student["age"] = 21                      # change a value
student["email"] = "aylin@example.com"   # add a new pair
print(student)

student.update({"age": 22, "course": "AI"})   # change or add several
print(student)

student = {"name": "Aylin", "age": 20, "email": "aylin@example.com"}
removed = student.pop("email")   # remove and give back the value
print(removed)
del student["age"]               # delete a pair
print(student)

student = {"name": "Aylin", "age": 20}
print(student.keys())
print(student.values())
print(student.items())
print(list(student.keys()))   # as a normal list

student = {"name": "Aylin", "age": 20}
print("name" in student)    # checks the KEYS
print("Aylin" in student)   # values are not checked
print("Aylin" in student.values())

course = {
    "title": "Python basics",
    "topics": ["variables", "data types", "operators"],
}
print(course["topics"])
print(course["topics"][1])

nums = {3, 1, 2, 3, 1}
print(nums)            # duplicates disappear

empty_set = set()      # an empty set
empty_dict = {}        # careful: {} is an empty DICT
print(type(empty_set))
print(type(empty_dict))

grades = [90, 85, 90, 70, 85]
unique = set(grades)
print(len(unique))      # how many different grades
print(sorted(unique))   # as a sorted list

s = {1, 2, 3}
s.add(4)        # add one item
s.add(2)        # already there: nothing changes
print(s)
s.remove(1)     # remove (error if missing)
s.discard(10)   # remove if present (no error)
print(s)

s = {1, 2, 3}
s.remove(10)

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}
print(a | b)   # union: in a OR b
print(a & b)   # intersection: in a AND b
print(a - b)   # difference: in a but not in b
print(b - a)
print(a ^ b)   # symmetric difference: in exactly one of them

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}
print(a.union(b))
print(a.intersection(b))
print(a.difference(b))
print(3 in a)

print(int("42"))      # text -> int
print(float("3.5"))   # text -> float
print(str(99))        # number -> text
print(int(7.9))       # float -> int: cuts the decimals
print(float(7))       # int -> float

print("5" + "5")             # text: glued together
print(int("5") + int("5"))   # numbers: added
print("5" * 3)               # text repeated

print(list("abc"))                  # text -> list of characters
print(tuple([1, 2, 3]))             # list -> tuple
print(set([1, 1, 2]))               # list -> set (duplicates removed)
print(list((4, 5)))                 # tuple -> list
print(dict([("a", 1), ("b", 2)]))   # pairs -> dict

print(int("3.5"))

print(int(float("3.5")))   # text -> float -> int

age_text = input("How old are you? ")   # input() ALWAYS gives text
age = int(age_text)                      # convert before doing maths
print("Next year you will be", age + 1)

a = 17
b = 5
print(a + b)    # add
print(a - b)    # subtract
print(a * b)    # multiply
print(a / b)    # divide (always a float)
print(a // b)   # floor division
print(a % b)    # remainder
print(a ** 2)   # power

n = 47
print(n % 2)        # remainder after dividing by 2
print(n % 2 == 0)   # True would mean "even"

total_minutes = 135
hours = total_minutes // 60     # whole hours
minutes = total_minutes % 60    # what is left over
print(f"{hours} h {minutes} min")

print(2 + 3 * 4)      # * before +
print((2 + 3) * 4)    # brackets first
print(10 - 4 - 3)     # left to right
print(-2 ** 2)        # ** before the minus sign!
print((-2) ** 2)

x = 10
x += 5     # x = x + 5
print(x)
x -= 3     # x = x - 3
print(x)
x *= 2     # x = x * 2
print(x)
x /= 4     # x = x / 4  (now a float)
print(x)

n = 7
n //= 2    # n = n // 2
print(n)
n **= 3    # n = n ** 3
print(n)
n %= 5     # n = n % 5
print(n)

greeting = "Hello"
greeting += ", Aylin"   # += also works on text
print(greeting)

print(5 == 5)
print(5 != 3)
print(3 > 5)
print(3 < 5)
print(5 >= 5)
print(4 <= 3)

print(5 == 5.0)              # same value
print("5" == 5)              # text is never equal to a number
print("apple" < "banana")    # text is compared alphabetically
print("Zebra" < "apple")     # capital letters come first!
print([1, 2] == [1, 2])      # lists compared item by item

age = 25
print(18 <= age < 65)   # same as: 18 <= age and age < 65

age = 20
has_ticket = True
is_vip = False

print(age >= 18 and has_ticket)              # both must be True
print(has_ticket or is_vip)                  # at least one
print(not is_vip)                            # flips the value
print(age >= 18 and (has_ticket or is_vip))  # brackets make it clear

print("py" in "python")                       # inside a string
print(3 in [1, 2, 3])                         # inside a list
print("grape" not in ["apple", "banana"])
print(5 in {1, 3, 5})                         # inside a set
print("name" in {"name": "Aylin"})            # dict: checks keys

result = None
print(result is None)      # the right way to check for None

a = [1, 2, 3]
b = [1, 2, 3]
c = a
print(a == b)    # same values?            True
print(a is b)    # the very same object?   False
print(a is c)    # c is just another name for a

print("Hello, Data Science!")

import sys
print(sys.version)

conda install package_name
pip install package_name

conda create -n my_project python
conda activate my_project

pip install notebook
jupyter notebook