Python Survival • Side A: Syntax

Variables • Logic • Loops • Data

1. Variables & Casting

x = 5          # int
y = 3.14       # float
name = "Dave"  # str
ok = True      # bool

Casting (Fix TypeErrors):

int("5") # 5   | str(5) # "5"
float(5) # 5.0 | bool(0) # False

2. Math (BEDMAS)

`**`	Exponent (Power)	1st
`* / // %`	Mult, Div, Floor, Mod	2nd
`+ -`	Add, Sub	3rd

10 // 3  # 3 (Floor Div)
10 % 3   # 1 (Remainder)
x += 1   # Increment

3. Logic & Control

if x > 10:
    print("Big")
elif x == 10:
    print("Exact")
else:
    print("Small")

`==` Equal	`!=` Not Eq
`and` Both True	`or` Any True
`not` Flip T/F	`in` Exists?

4. Loops (Repetition)

While Loop:

c = 0
while c < 5:
    print(c)
    c += 1 # Update!

For Loop (Range):

# 0 to 4
for i in range(5): ...
# 2, 4, 6, 8 (Stop=10 excl)
for i in range(2, 10, 2): ...
# 5, 4, 3, 2, 1 (Reverse)
for i in range(5, 0, -1): ...

5. Functions

def add(a, b):
    res = a + b
    return res # Sends back

x = add(5, 2) # x becomes 7

⚠️ Vars inside functions are LOCAL (invisible outside).

6. Strings (Immutable)

s = " Code "
s[0]      # ' ' (Index 0)
s[-1]     # ' ' (Last)
s[1:5]    # 'Code' (Slice)
len(s)    # 6

.strip()	Kill whitespace
.lower()	" code "
.upper()	" CODE "
.replace("o","a")	" Cade "
.find("d")	Index (3)

msg = f"Val: {x}" # F-String

7. Lists (Mutable [])

L = [10, 20, 30]
L[0] = 99     # [99, 20, 30]
L.append(40)  # Add to end

.pop(i)	Remove at index
.remove(v)	Remove value
.insert(i,v)	Add at index
.sort()	Order A-Z
v in L	Check exists

8. Dictionaries (Key:Val)

d = {"name": "Jo", "age": 20}
val = d["name"]       # "Jo"
d["city"] = "NY"      # Add
safe = d.get("id", 0) # No crash

Looping:

for k, v in d.items():
    print(k, v)

9. Files (Read/Write)

with open("file.txt", "r") as f:
    lines = f.readlines()
    for line in lines:
        print(line.strip())

"w"=Overwrite, "a"=Append

10. Error Handling

try:
    x = 10 / 0
except ZeroDivisionError:
    print("Bad Math")
except ValueError:
    print("Bad Type")

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Python Survival • Side B: Recipes

Algorithms • Patterns • Models

Algorithm: Accumulator (Sum/Count)

Goal: Add up numbers or count items.

total = 0       # 1. Initialize
count = 0
nums = [10, 20, 5, 40]

for n in nums:  # 2. Loop
    total += n  # 3. Accumulate
    count += 1  # 3. Count

print(f"Avg: {total/count}")

Algorithm: Find Max/Min

Goal: Find largest item without max().

nums = [5, 2, 9, 1]
highest = nums[0]  # Assume 1st is max

for n in nums:
    if n > highest: # Found new max?
        highest = n # Update it

print(highest) # 9

Algorithm: Safe Input Loop

Goal: Force user to give valid integer.

while True:
    val = input("Enter 1-10: ")
    
    # 1. Check if digits
    if val.isdecimal():
        num = int(val)
        
        # 2. Check Range
        if 1 <= num <= 10:
            print("Valid!")
            break # Exit loop
        else:
            print("Out of range")
    else:
        print("Not a number")

Algorithm: Filter List

Goal: Copy only even numbers to new list.

old = [1, 2, 3, 4]
new_list = []

for n in old:
    if n % 2 == 0:     # Check even
        new_list.append(n)

print(new_list) # [2, 4]

Reference: The Hierarchy

When in doubt, use Parentheses.

Order	Operator	Desc
1. KING	`( )`	Parentheses
2. Power	`**`	Exponents
3. Sign	`-x, +x`	Positive/Neg
4. Math	`* / // %`	Mult/Div
5. Math	`+ -`	Add/Sub
6. Compare	`== > <`	Relational
7. Logic	`not`	Logical Not
8. Logic	`and`	Logical And
9. Logic	`or`	Logical Or

Design: Flowcharts & IPO

Flowchart Symbols:

🟢 Oval
Start / End

▱ Parallelogram
Input / Output

▭ Rectangle
Process / Calc

◇ Diamond
Decision (If)

IPO Model:

Input: User data (params)
Process: The logic/math
Output: The result (return/print)

Useful Built-in Functions

abs(-5)	5 (Positive)
round(3.6)	4 (Nearest)
round(3.14, 1)	3.1 (1 decimal)
max(1, 2)	2 (Largest)
min(1, 2)	1 (Smallest)
len(obj)	Length
type(x)	Check Type

Module: Random

import random

# Random Int (Inclusive)
x = random.randint(1, 10)

# Random Float (0.0 - 1.0)
y = random.random()

"I can fail math and still pass."
- Famous Last Words, 2025

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