Python Basic Syntax Elements

December 20, 2024 · 3 min read · Page View:

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Sometimes you may forget about the basic of Python, so let us take a look at the summary of Python basic summary. The content of this review is as follows: data type, variable, control flow, input & output, PEP8 format.

CH1 Basic Syntax Elements #

1 Data Type #

Basic Type: Number, String, Boolean #

Number Type

• int
• float
• complex (a+bj)

String Type

• str: use " " or ' '

Boolean Type

• bool

y = 2 < 1
y
# False

Composite Type: List, Tuple, Dictionary, Set #

List Type, ordered

a = [1, 2, 3, 4, 5]
a[4]
# 5

Tuple Type, ordered, elements are not modifiable

b = (1, 2, 3, 4, 5)
b[0]
# 1

Dictionary Type, key-value mapping, unordered

student = {201901: "john", 201902: "howe", 201903: "timerring"}
student[201902]
# 'howe'

Set Type, a collection of unique elements, unordered

s = {"john", "howe", "timerring", "john"}
s
# {'john', 'howe', 'timerring'}

2 Variable #

Variable Naming #

What can be used as variable names?

• uppercase letters, lowercase letters, numbers, underscores, and Chinese characters.
• strictly case-sensitive

What is not allowed?

• the first character cannot be a number
• there cannot be spaces in the middle of the variable name
• cannot be the same as the 33 Python reserved words

Variable Name Definition Techniques

• underscore (variable and function name) variable name consists of multiple words: use _ to connect multiple words

age_of_students = [17, 18, 19]

• Camel Case (class name) variable name consists of multiple words: capitalize the first letter of each word

AgeOfStudents

• Constant (e.g. $\pi$, e) variable name all letters are uppercase

MAX_ITERATION = 1000

Variable Assignment #

x, y = 1, 2 # separated by ","
print(x, y)
x, y = y, x
print(x, y)

3 Control Flow #

Loop (for) #

res = 0
for i in [1,2,3,4,5]:
    res += i
res
# 15

Loop (while) #

i = 1
res = 0
while i <= 5:
    res += i
    i += 1
res
# 15

Branch (if) #

if condition:
    execute statement
else:
    execute statement

4 Input & Output #

Data Input #

External File Import

• from local disk, network, etc. See File, Exception, and Module.

Dynamic Interactive Input

x = input("please input: ")
type(x)
# str, so the addition is string concatenation

Use eval() to remove the quotes

x = eval(input("please input: "))
type(x)
# int

Data Output #

Print #

Each print() defaults to a newline

print("timerring")
# timerring
print(1)
# 1

Line Break Control end= #

print(123,end=" ")# also can customize the end content
print(456)
# 123 456

Combined Output #

PI = 3.1415926
E = 2.71828
print("PI = ", PI, "E = ", E)

Formatting Output #

# one-to-one correspondence
print("PI = {0},E = {1}".format(PI, E))
# PI = 3.1415926,E = 2.71828
print("PI = {0},E = {0}".format(PI, E))
# PI = 3.1415926,E = 3.1415926
# default order
print("PI = {},E = {}".format(PI, E))
# PI = 3.1415926,E = 2.71828

Decorative Output #

Padding Output

print("{0:_^20}".format(PI)) # 0 is the variable PI, : is the modifier output, _ is the modifier character, ^ is centered, 20 is the output width
# ____3.1415926_____   padding
print("{0:*<30}".format(PI)) # < is left-aligned
# 3.1415926*********************

Thousands Separator

print("{0:,}".format(10000000))
# 10,000,000

Simplified Floating Point Output #

• keep 2 decimal places

print("{0:.2f}".format(PI))
# 3.14

• Output as a percentage

print("{0:.1%}".format(0.818727))
# 81.9%

• Scientific Notation Output

print("{0:.2e}".format(0.818727))
# 8.19e-01

Integer Base Conversion Output

• Decimal to Binary, Unicode, Decimal, Octal, Hexadecimal

"Binary {0:b}, Unicode {0:c}, Decimal {0:d}, Octal {0:o}, Hexadecimal {0:x}".format(450)
# Binary 11100010, Unicode \u1b6, Decimal 450, Octal 702, Hexadecimal 1c2

Summary #

• Formatting Output: "character{0:modifier}character{1:modifier}character".format(v0, v1)

• Modifier Output: must be strictly in order.

5 Program Format (PEP8 Format) #

Line Maximum Length #

All lines are limited to a maximum of 79 characters

Indentation #

• Use indentation to represent the logical relationship between statements, indentation: 4 characters

Use Spaces #

• Add a space on both sides of the binary operator
• Add spaces around different priority operators

x = x*2 - 1
c = (a+b) * (a-b)

• Use spaces after commas

Avoid Using Spaces #

• Do not add spaces around = when specifying keyword arguments or default parameter values

def fun(n=1, m=2):
    print(n, m)

Comments #

• Single-line comment # comment content

• Multi-line comment """comment content, can be split into multiple lines"""