Essential Python Programming Snippets

File Handling

# Basic file reading
file = open("data.txt", "r")
content = file.read()          # Read entire file
lines = file.readlines()       # Read as list of lines
file.close()

# Reading line by line
file = open("data.txt", "r")
for line in file:
    print(line.strip())        # strip() removes \n
file.close()

# Write to file (overwrites)
file = open("output.txt", "w")
file.write("Hello World\n")
file.close()

# Append to file (adds to end)
file = open("output.txt", "a")
file.write("New line\n")
file.close()

Working with Lists

# Creating lists
numbers = [1, 2, 3, 4, 5]
names = ["John", "Maria", "Carlos"]

# Accessing elements
first = numbers[0]            # First element
last = numbers[-1]            # Last element
slice = numbers[1:4]         # Elements 1 to 3

# List methods
numbers.append(6)             # Add to end
numbers.remove(3)             # Remove value
length = len(numbers)         # Get length

Loops

# For loop through list
for number in numbers:
    print(number)

# For loop with index
for i in range(len(numbers)):
    print(f"Index {i}: {numbers[i]}")

# While loop
count = 0
while count < 5:
    print(count)
    count += 1

String Operations

text = "  Hello World  "
text.strip()                  # "Hello World" - remove spaces
text.lower()                  # "  hello world  " - lowercase
text.upper()                  # "  HELLO WORLD  " - uppercase
text.split()                  # ["Hello", "World"] - split by space
text.split(",")               # Split by comma
text.replace("H", "J")        # "  Jello World  "

Conditionals and Comparisons

if temperature > 30:          # Basic conditions if/else
    print("Hot")
elif temperature > 20:
    print("Warm")
else:
    print("Cold")

# Common comparisons
x == y    # Equal to
x != y    # Not equal to
x > y     # Greater than
x < y     # Less than
x >= y    # Greater or equal

Math and Statistics

max_value = max([10, 5, 8, 20])    # Returns 20 - Finding max/min
min_value = min([10, 5, 8, 20])    # Returns 5

# Average calculation
numbers = [10, 20, 30]
total = sum(numbers)              # Or use loop:
total = 0
for num in numbers:
    total += num
average = total / len(numbers)

Data Processing

# Read CSV (name,grade format)
file = open("data.csv", "r")
for line in file:
    parts = line.strip().split(",")
    name = parts[0]
    grade = float(parts[1])
    # Process data...
file.close()

Dictionaries

word_count = {}
for word in words:
    if word in word_count:
        word_count[word] += 1
    else:
        word_count[word] = 1