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Python Cheat Sheet
Contents
- Variables and Data Types
- Input and Output
- Arithmetic Operators
- Comparison Operators
- Logical Operators
- Membership Operators
- If elif else
- String Operations
- Functions
- While Loop
- For Loop
- List and Operations
- Tuples
- Set
- Dictionary
- Exception Handling
- File Handling
- Common Built-in Functions
Variables and Data Types
name = "John" # string -> str
age = 30 # number -> int
weight = 63.5 # number -> float
married = True # Boolean -> bool
Input and Output
# Read Input from terminal window
name = input("Enter Name") # -> John
# Write name to terminal window
print(name) # -> John
Arithmetic Operators
x = 10
y = 3
z = x + y # addition -> 13
z = x - y # subtraction -> 7
z = x * y # multiplication -> 30
z = x / y # true division -> 3.3333
z = x // y # floor division -> 3
z = x ** y # exponent -> 1000
z = x % y # modulo division -> 1
Comparison Operators
x = 10
y = 5
z = (x == y) # Equal to -> False
z = (x != y) # Not equal to -> True
z = (x > y) # Greater than -> True
z = (x < y) # Less than -> False
z = (x >= y) # Greater than or equal to -> True
z = (x <= y) # Less than or equal to -> False
Logical Operators
x = 10
y = 5
z = 15
result = (x > y) and (z > y) # and -> True (both conditions true)
result = (x > y) or (z < y) # or -> True (any one condition true)
result = not (x > y) # not -> False (negate condition)
Membership Operators
fruits = ["apple", "banana", "cherry"]
name = "python"
result = "banana" in fruits # in -> True
result = "mango" in fruits # in -> False
result = "python" in name # in -> True
result = "java" not in name # not in -> True
result = "banana" not in fruits # not in -> False
If elif else
if number > 0:
print(f"{number} -> Positive")
elif number == 0:
print(f"{number} -> Zero")
else:
print(f"{number} -> Negative")
String Operations
text = " Hello Python World! "
print(text.upper()) # HELLO PYTHON WORLD!
print(text.lower()) # hello python world!
print(text.strip()) # Hello Python World!
print(text.split()) # ['Hello', 'Python', 'World!']
fruits = ["apple", "banana", "cherry"]
print(", ".join(fruits)) # apple, banana, cherry
print("Python".find("th")) # 2
print("Python".find("java")) # -1
name = "John"
print("Hello, {}".format(name)) # Hello, John
print(f"Hello, {name}!") # Hello, John!
Functions
def greet():
print("Hello World!")
def hello(name):
print("Hello", name)
def add(x, y):
return x + y
def increment(x, y = 1)
return x + y
greet() # Hello World!
hello("John") # Hello John!
total = add(10, 20)
print(total) # 30
result = increment(10)
print(result) # 11
While Loop
i = 1 # Start
while i <= 10: # Stop when i > 10
print(i)
i = i + 1 # Step
For Loop
for i in range(1, 11, 1): # Start -> 1, Stop -> 11, Step -> 1
print(i)
List
- Lists are non-primitive data type to hold multiple items.
- Can contain any types and number of items
- Can have duplicates
- Mutable - Can modify values
- Allows zero based index read and write
List Operations
numbers = [10, 30, 20, 40]
numbers.append(50) # [10, 30, 20, 40, 50]
numbers.insert(1, 15) # [10, 15, 30, 20, 40, 50]
numbers.extend([60, 70]) # [10, 15, 30, 20, 40, 50, 60, 70]
numbers.pop() # removes 70
numbers.pop(2) # removes 30
numbers.clear() # []
nums = [4, 1, 3, 2]
nums.sort() # [1, 2, 3, 4]
nums.reverse() # [4, 3, 2, 1]
List Slicing
numbers = [10, 20, 30, 40, 50, 60, 70, 80]
numbers[0] # 10
numbers[-1] # 80
numbers[2:5:1] # [30, 40, 50]
numbers[:4] # [10, 20, 30, 40]
numbers[3:] # [40, 50, 60, 70, 80]
numbers[::-1] # [80, 70, 60, 50, 40, 30, 20, 10] reverse
List Comprehension
numbers = [1, 2, 3, 4, 5]
print(numbers) # [1, 2, 3, 4, 5]
square = [x**2 for x in numbers]
print(square) # [1, 4, 9, 16, 25]
Tuples
- Immutable, can not modify after creation
- Faster than list
# Creating a tuple
colors = ("red", "green", "blue", "yellow")
print(colors) # ('red', 'green', 'blue', 'yellow')
print(type(colors)) # <class 'tuple'>
Set
- Can not have duplicates
- Mutable
nums = {1, 2, 3, 4, 5}
nums.add(6) # Add single item
nums.update([7, 8, 9]) # Add multiple items
nums.remove(3) # Remove item (error if not found)
nums.discard(10) # Remove item (no error if not found)
print(len(nums)) # 8
Dictionary
- Key, Value Pairs
- Commonly used as look-up table
student = {
"name": "John",
"age": 20,
"grade": "A",
"city": "Chennai"
}
print(student)
print(student["name"]) # John
print(student.get("age")) # 20
student["age"] = 21 # Update value
student["country"] = "India" # Add new key-value
print(student.keys()) # ['name', 'age', 'grade', 'city', 'country']
print(student.values()) # ['John', 21, 'A', 'Chennai', 'India']
print(student.items()) # [('name', 'John'), ...]
del student["city"] # Delete a key
student.pop("grade") # Remove and return value
student.clear() # Remove all items
Exception Handling
try:
result = 10 / 0
except ZeroDivisionError:
print("Cannot divide by zero")
try:
x = "10"
y = "ABC"
result = int(x) / int(y)
except ValueError:
print("Invalid input, can not convert to int")
finally:
print("Clean up resources in finally")
File Handling
Read Mode
- throws error when file not found
file = open("Quotes.txt", "r") # r - Read
all_string = file.read()
one_line = file.readline()
all_lines = file.readlines()
file.close()
Write Mode
- Create file when not present
- Caution overwrites when file already exists
file = open("Quotes.txt", "w") # w - Write
file.write("Hello from python")
file.writelines(["First Line\n", "Second Line\n"])
file.close()
Append Mode
- Create file when not present
- Appends to existing file.
file = open("Quotes.txt", "a") # a - append
file.write("Hello from python")
file.writelines(["First Line\n", "Second Line\n"])
file.close()
Common Built-in Functions
len(), sum(), min(), max(), sorted(), type(str), dir(list)