Master Python Basics: Variables, Data Types, and Core Syntax

Python Basics Overview

Python is an interpreted, object‑oriented language that runs on Windows, macOS, and Linux. It offers an interactive shell, simple syntax, and powerful built‑in features.

Key Features

Interpreted language – no compilation needed.

Interactive command line.

Object‑oriented programming.

Cross‑platform compatibility.

Simple yet powerful.

Variables

Variables act as containers for values. Names may contain letters, digits, and underscores but cannot start with a digit and are case‑sensitive.

Python is weakly typed; you do not declare a type when creating a variable.

Data Types

Common built‑in types include:

Numbers – integers and floating‑point numbers.

# integer a = 1
# float b = 2.1
print a, b

Strings – text enclosed in single or double quotes.

c = 'Hello'
d = '你好'
print c, d

Use + to concatenate and len() to get length. Slicing accesses substrings.

Lists – ordered collections that can hold any type.

a = []
a.append(1)
a.append(2.1)
a.append('Hello')
print a
print len(a)
print a[1], a[-1]
a[1] = 100
print a
del a[0]
print a

Tuples – immutable ordered collections.

a = (1, 2.1, 'Hello')
# a[0] = 100  # raises error

Dictionaries – key‑value mappings accessed by keys.

di = {}
di['k1'] = 1
di['k2'] = 2.1
di['k3'] = 'Hello'
print di['k1']
print di.has_key('k4')  # False

Comments

Use # for single‑line comments and triple quotes '''...''' for block comments. In Sublime Text, select code and press Ctrl+/ to toggle comments.

Reserved Words

Avoid using Python keywords such as import, class, etc., as variable names.

Indentation

Code blocks are defined by indentation rather than braces. Consistent indentation is required for if, while, for, try, etc.

Operators

Arithmetic: +, -, *, /, % Comparison: ==, !=, >, <, >=, <= Assignment: =, +=, -=, *=, /=, %= Logical: and, or,

not

Conditional Statements

a = 1
if a == 1:
    print '11111'
else:
    print '33333'

if a == 1:
    print '11111'
elif a == 2:
    print '22222'
else:
    print '33333'

Loops

While loop repeats while a condition is true.

flag = 1
while flag < 10:
    print flag
    flag += 1

For loop iterates over a range or iterable.

for x in xrange(0, 10):
    print x

for item in li:
    print item
for key in di.keys():
    print key
for key, value in di.items():
    print key, value

Loop control statements include pass, continue, and break.

for x in xrange(0, 10):
    if x == 5:
        pass
    else:
        print x

Time Handling

Python represents time as a timestamp – seconds since 1970‑01‑01 00:00:00 UTC.

import time
t = time.time()
print t, type(t)
# Convert string to timestamp
s = '2016-10-01 10:00:00'
ts = int(time.mktime(time.strptime(s, '%Y-%m-%d %H:%M:%S')))
print ts
# Convert timestamp to string
now = int(time.time())
print time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(now))

File I/O

# Write file
fw = open('data.txt', 'w')
for x in xrange(0, 10):
    fw.write(str(x) + '
')
fw.close()
# Read file
fr = open('data.txt', 'r')
for line in fr:
    print line.strip()
fr.close()

Exception Handling

try:
    print 1 / 0
except Exception as e:
    print e
else:
    print 'No error'
finally:
    print 'Always runs'

Functions

Functions encapsulate reusable code and may accept parameters.

def hello(name1, name2):
    print 'Hello ' + name1 + ' ' + name2

hello('Python', 'JavaScript')