Python Basics: Comments, Indentation, Variables, Data Types, Operators, Strings, Lists, Conditionals, Loops, and Functions

Before diving into statistical analysis with Python, it is essential to master the basic syntax and common operations of the language. This guide consolidates the most frequently used Python constructs to help beginners quickly become familiar with core concepts.

1. Comments and Indentation

Comments

Comments do not affect program execution and improve readability.

Single‑line comments start with # :

<code># comment on its own line
print("Python statistical analysis")  # print output</code>

Running the above prints:

<code>Python statistical analysis</code>

Indentation

Python uses indentation to define code blocks. The PEP 8 style guide recommends four spaces per level and discourages mixing spaces with tabs.

Although any number of spaces or tabs can technically be used, it is strongly recommended to follow the PEP 8 guideline of using 4 spaces as the indentation unit.

All statements in the same block must have the same indentation:

<code>if True:
    print("True")
else:
    print("False")</code>

Inconsistent indentation causes a runtime error:

<code>if True:
    print("Answer")
    print("True")
else:
    print("Answer")
  print("False")  # Indentation mismatch</code>

2. Variable Naming

Python variables are created by assignment without explicit type declaration:

<code>x = 10      # integer
y = "Python statistical analysis"  # string
z = 3.14    # float</code>

Rules

Names may contain letters (A‑Z, a‑z), digits (0‑9), and underscores ( _ ).

The first character must be a letter or underscore; it cannot be a digit.

Variable names are case‑sensitive ( myVariable ≠ myvariable ).

Names cannot be Python reserved keywords (e.g., for , if , while , class ).

Use meaningful names; follow PEP 8 by using lowercase words separated by underscores, e.g., employee_name instead of EmployeeName or employeename .

3. Data Types

Numeric Types

int : arbitrary‑size integers, e.g., 123 , -456 .

float : floating‑point numbers, e.g., 3.14 , -2.0 .

complex : numbers with real and imaginary parts, e.g., 3+2j .

Boolean

Two values: True and False .

String ( str )

Text enclosed in single or double quotes, e.g., "Hello, World!" .

Sequence Types

list ( [] ): ordered, mutable collection, e.g., [1, 2, "three"] .

tuple ( () ): ordered, immutable collection, e.g., (1, 2, 3) .

Mapping Type

dict ( {} ): unordered key‑value pairs, e.g., {"name": "Alice", "age": 25} .

Set Type

set ( {} for non‑empty sets, set() for an empty set) stores unordered, unique elements.

Other Special Types

NoneType ( None ) represents the absence of a value.

4. Type Conversion

Implicit Conversion

When mixing types, Python automatically promotes to the higher‑precision type:

<code>num_int = 123
num_flo = 1.23
num_new = num_int + num_flo
print("num_int type:", type(num_int))
print("num_flo type:", type(num_flo))
print("num_new value:", num_new)
print("num_new type:", type(num_new))</code>

Explicit Conversion

Use built‑in functions such as int() , float() , str() :

<code>x = int(1)      # 1
y = int(2.8)    # 2
z = int("3")   # 3
print(x, type(x))
print(y, type(y))
print(z, type(z))
</code>

5. Operators

Arithmetic

Assuming a = 10 and b = 21 :

Operator

Description

Example

+

Addition

a + b → 31

-

Subtraction

a - b → -11

*

Multiplication

a * b → 210

**

Exponentiation

a ** b → 10⁽²¹⁾

/

Division

b / a → 2.1

//

Floor division

b // a → 2

%

Modulo

b % a → 1

Comparison

With a = 10 , b = 20 :

Operator

Description

Result

==

Equal

(a == b) → False

!=

Not equal

(a != b) → True

>

Greater than

(a > b) → False

<

Less than

(a < b) → True

>=

Greater or equal

(a >= b) → False

<=

Less or equal

(a <= b) → True

Assignment

Common operators include = , += , -= , *= , /= , %= , **= , //= .

6. Strings

Creation

<code>str1 = 'Hello, World!'
str2 = "This is also a string."
</code>

Access

<code>greeting = "Hello!"
first_char = greeting[0]  # 'H'
</code>

Slicing

<code>sub_str = greeting[0:5]  # 'Hello'
</code>

Length

<code>length = len(greeting)  # 6
</code>

Concatenation and Repetition

<code>name = "Alice"
message = "Hi, " + name + "!"
repeated = "Python " * 3  # 'Python Python Python '
</code>

Formatting

<code>num = 42
formatted = f"The answer is {num}"  # f-string
</code>

Common Methods

lower() , upper()

strip()

split()

join()

find() , index()

replace(old, new)

7. Lists

Creation

<code>empty_list = []
numbers_list = [1, 2, 3, 4, 5]
mixed_list = [1, "apple", True, None]
another_list = list(("a", "b", "c"))
</code>

Access and Slicing

<code>lst = ["apple", "banana", "cherry"]
first_item = lst[0]   # 'apple'
last_item = lst[-1]   # 'cherry'
sublist = lst[1:3]    # ['banana']
</code>

Modification

<code>lst[0] = "grape"
lst.append("date")
lst.insert(0, "kiwi")
removed = lst.pop()      # last element
lst.pop(0)               # remove first element
lst.remove("apple")
lst.extend([6,7])
lst.sort()
lst.reverse()
len_lst = len(lst)
count = lst.count("banana")
</code>

8. Conditional Statements

<code>if condition:
    # true block
elif other_condition:
    # else‑if block
else:
    # false block
</code>

Example:

<code>temperature = 25
if temperature > 20:
    print("It's warm outside.")
</code>

9. Loop Statements

while Loop

<code>count = 0
while count < 5:
    print(count)
    count += 1
</code>

for Loop

<code>numbers = [1, 2, 3, 4, 5]
for number in numbers:
    print(number)
</code>

Control keywords:

break – exit the loop immediately.

continue – skip the rest of the current iteration.

<code>for i in range(10):
    if i % 2 == 0:
        continue  # skip even numbers
    print(i)      # prints odd numbers

j = 0
while j < 10:
    j += 1
    if j == 5:
        break   # exit when j reaches 5
    print(j)
</code>

10. Custom Functions

<code>def greet(name):
    print(f"Hello, {name}!")

greet("Bob")  # Output: Hello, Bob!
</code>

Function definition uses the def keyword, optional parameters, default values, and variable‑length arguments ( *args , **kwargs ). Functions may return a value with return ; otherwise they return None .

Parameter Types

Required positional parameters.

Keyword parameters (named arguments).

Default parameters with preset values.

Variable‑length parameters: *args for extra positional arguments, **kwargs for extra keyword arguments.

<code>def add_numbers(*nums):
    total = sum(nums)
    return total

result = add_numbers(1,2,3,4)
print(result)  # 10
</code>

References

Python 3 Tutorial | 菜鸟教程

Python Official Documentation