Python Basics

#EN

Introduction

In this article, I'll try to dig deeper into Python Basics.

Mutable vs Immutable

Mutable

  • The object ids are same
a = [1,2,3]

print("a = %s" % a)
print("id(a) = %s" % id(a))

a.append(4)

print("a = %s" % a)
print("id(a) = %s" % id(a))

a = [1, 2, 3]
id(a) = 4397053320
a = [1, 2, 3, 4]
id(a) = 4397053320

Immutable

  • The object ids are changed
a = "abc"

print("a = %s" % a)
print("id(a) = %s" % id(a))

a = a + "def"

print("a = %s" % a)
print("id(a) = %s" % id(a))

a = abc
id(a) = 4432244216
a = abcdef
id(a) = 4434341816

Variable

classImmutable
bool✅
int✅
float✅
list
tuple✅
str✅
set
frozenset✅
dict

Multiple variable

Mutable

a = [1,2,3]
b = a

a.append(4)

print ("a = %s" % a)
print ("b = %s" % b)

a = [1, 2, 3, 4]
b = [1, 2, 3, 4]

Immutable

a = "abc"
b = a

a = a + "def"

print ("a = %s" % a)
print ("b = %s" % b)

a = abcdef
b = abc

Python Conveniences

Conditional Expressions

# Case 1
if n >= 0:
  param = n
else:
  param = −n

result = foo(param) # call the function

# Case 2
param = n if n >= 0 else −n # pick the appropriate value
result = foo(param)

Comprehension Syntax

# Case 1
result = []
for k in range(1, n+1):
  if n % k == 0:
    result.append(k)

# Case 2
result = [k for k in range(1, n+1) if n % k == 0]

Packing and Unpacking of Sequences

for x, y in [ (7, 2), (5, 8), (6, 4) ]:
for k, v in mapping.items():

Simultaneous Assignments

j = 1
k = 2
id(j) # 4343226616
id(k) # 4343226648

j,k = k, j

id(j) # 4343226648
id(k) # 4343226616
j # 2
k # 1

Modules and the Import Statement

  • If the module is imported from another scripts, the code under if name == __main__ : is not executed
  • It is executed only when if the module is directly invoked as a script
if name == __main__ :

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