Built-in Methods for Numeric Types (int and float)

The int() and float() functions are used for type creation and conversion.

# Type definition
age = 10  # Equivalent to age = int(10)
salary = 3000.3  # Equivalent to salary = float(3000.3)

# Type conversion
s = '123'
res = int(s)  # Converts string of integers to int
print(res, type(res))  # Output: (123, <class 'int'>)

# Error demonstration
# int('12.3')  # ValueError: invalid literal for int() with base 10: '12.3'

# Base conversion
print(bin(3))  # Decimal to binary: '0b11'
print(oct(9))  # Decimal to octal: '0o11'
print(hex(17))  # Decimal to hexadecimal: '0x11'

# Convert from other bases to decimal
print(int('0b11', 2))  # Output: 3
print(int('0o11', 8))  # Output: 9
print(int('0x11', 16))  # Output: 17

# Float conversion
val = '12.3'
result = float(val)
print(result, type(result))  # Output: (12.3, <class 'float'>)

Numeric types primarily support mathematical and comparison operations and do not have many built-in methods beyond these functions.

String Data Type

String literals can be created using single quotes, double quotes, or triple quotes.

name_1 = 'jason'
name_2 = "lili"
name_3 = """ricky"""

Type Conversion

The str() function can convert any data type to a string.

print(type(str([1, 2, 3])))  # list -> str
print(type(str({'name': 'jaswe', 'age': 18})))  # dict -> str
print(type(str({1, 2, 3})))  # set -> str
print(type(str((1, 2, 3))))  # tuple -> str

Fundamental Operasions

text = 'hello python!'

# 1. Indexing
print(text[6])    # 'p' (forward indexing)
print(text[-4])   # 'h' (reverse indexing)
# text[0] = 'H'  # Error: strings are immutable

# 2. Slicing
print(text[0:9])     # 'hello pyt' (slice from 0 to 8)
print(text[0:9:2])   # 'hlopt' (step of 2)
print(text[::-1])    # '!nohtyp olleh' (reverse)

# 3. Length
print(len(text))     # 13

# 4. Membership tests
print('hello' in text)      # True
print('tony' not in text)   # True

Key String Methods

1. strip(), lstrip(), rstrip()

str_1 = '###Erfd###'
print(str_1.strip('#'))   # 'Erfd' (both sides)
print(str_1.lstrip('#'))  # 'Erfd###' (left side)
print(str_1.rstrip('#'))  # '###Erfd' (right side)

2. lower(), upper()

str_2 = 'saEFDfef'
print(str_2.lower())  # 'saefdfef'
print(str_2.upper())  # 'SAEFDFEF'

3. startswith(), endswith()

str_3 = 'tony jam'
print(str_3.startswith('t'))  # True
print(str_3.endswith('t'))    # False

4. format()

# Keyword arguments
str_4 = 'name:{name}, age:{age}'.format(age=18, name='sfv')
print(str_4)  # 'name:sfv, age:18'

# Positional arguments
str_5 = 'name:{}, age:{}'.format('asdf', 12)
print(str_5)  # 'name:asdf, age:12'

# Indexed arguments
str_6 = 'name:{1}, age:{0}'.format(12, 'dsdf')
print(str_6)  # 'name:dsdf, age:12'

5. split(), rsplit()

path = 'c:/sdw/ds/dw/ac/sd.txt'
print(path.split('/', 1))   # ['c:', 'sdw/ds/dw/ac/sd.txt'] (left to right)
print(path.rsplit('/', 1))  # ['c:/sdw/ds/dw/ac', 'sd.txt'] (right to left)

6. join()

print('#'.join('sefdgs'))  # 's#e#f#d#g#s'
print('|'.join(['tony', '18', 'read']))  # 'tony|18|read'

7. replace()

str_7 = 'my name is tony, my age is 18!'
print(str_7.replace('18', '34'))  # 'my name is tony, my age is 34!'
print(str_7.replace('my', 'MY', 1))  # 'MY name is tony, my age is 18!'

8. isdigit()

print('235235'.isdigit())   # True
print('235223sf35'.isdigit())  # False

Additional String Methods

1. find() and rfind()

sample = 'tonr asr dfeei sccof'
print(sample.find('o', 0, 13))  # 1 (returns index, -1 if not found)
# .index() is similar but raises ValueError if not found

2. count()

print(sample.count('o'))  # 2

3. center(), ljust(), rjust(), zfill()

name = 'sdacd'
print(name.center(30, '-'))   # '------------sdacd------------'
print(name.rjust(30, '@'))    # '@@@@@@@@@@@@@@@@@@@@@@@sdacd'
print(name.ljust(30, '#'))    # 'sdacd#########################'
print(name.zfill(50))         # '000000000000000000000000000000000000000000sdacd'

4. expandtabs()

print('tony\thello')  # 'tony    hello' (\t expands to tab)

5. capitalize(), swapcase(), title()

example = 'hello xIanG mo yu'
print(example.capitalize())  # 'Hello xiang mo yu'
print(example.swapcase())    # 'HELLO XiANg MO YU'
print(example.title())       # 'Hello Xiang Mo Yu'

6. Numeric checks

# Different methods for checking numeric characters
num1 = '4'      # ASCII digit
num2 = '四'     # Chinese numeral
num3 = 'Ⅳ'     # Roman numeral

print(num1.isdigit())    # True
print(num2.isdigit())    # False
print(num3.isdigit())    # False

print(num1.isdecimal())  # True
print(num2.isdecimal())  # False
print(num3.isdecimal())  # False

print(num1.isnumeric())  # True
print(num2.isnumeric())  # True
print(num3.isnumeric())  # True

List Data Type

Lists are defined within square brackets and can contain elements of any data type.

list_1 = [1, 'a', [1, 2]]  # Equivalent to list([1, 'a', [1, 2]])

Type Conversion

Any iterable can be converted to a list using list().

print(list('wdad'))           # ['w', 'd', 'a', 'd']
print(list([1, 2, 3]))        # [1, 2, 3]
print(list({'name': 'jason', 'age': 18}))  # ['name', 'age']
print(list((1, 2, 3)))        # [1, 2, 3]
print(list({1, 2, 3, 4}))    # [1, 2, 3, 4]

List Operations

1. Indexing and Assignment

friends = ['tony', 'jason', 'tom', 4, 5]
print(friends[0])      # 'tony'
print(friends[-1])     # 5
friends[1] = 'martthow'  # Lists are mutable
print(friends)         # ['tony', 'martthow', 'tom', 4, 5]

2. Slicing

print(friends[0:4])    # ['tony', 'martthow', 'tom', 4]
print(friends[0:4:2])  # ['tony', 'tom'] (step of 2)

3. Length

print(len(friends))    # 5

4. Membership tests

print('tony' in friends)      # True
print('xxx' not in friends)   # True

5. Adding Elements

# append() adds to the end
list_a = ['a', 'b', 'c']
list_a.append('d')
print(list_a)  # ['a', 'b', 'c', 'd']

# extend() adds multiple elements
list_a.extend(['e', 'f'])
print(list_a)  # ['a', 'b', 'c', 'd', 'e', 'f']

# insert() adds at specific position
list_a.insert(0, 'first')
print(list_a)  # ['first', 'a', 'b', 'c', 'd', 'e', 'f']

6. Removing Elmeents

# del statement
list_b = [11, 22, 33, 44]
del list_b[2]
print(list_b)  # [11, 22, 44]

# pop() removes and returns element
list_c = [11, 22, 33, 22, 44]
removed = list_c.pop()
print(removed)  # 44
print(list_c)   # [11, 22, 33, 22]

removed = list_c.pop(1)
print(removed)  # 22
print(list_c)   # [11, 33, 22]

# remove() deletes by value
list_d = [11, 22, 33, 22, 44]
list_d.remove(22)  # Removes first occurrence
print(list_d)      # [11, 33, 22, 44]

7. reverse()

list_e = [11, 22, 33, 44]
list_e.reverse()
print(list_e)  # [44, 33, 22, 11]

8. sort()

list_f = [11, 22, 3, 42, 7, 55]
list_f.sort()
print(list_f)  # [3, 7, 11, 22, 42, 55] (ascending)

list_g = [11, 22, 3, 42, 7, 55]
list_g.sort(reverse=True)
print(list_g)  # [55, 42, 22, 11, 7, 3] (descending)

9. Iteration

for item in friends:
    print(item)

Lists can be compared lexicographically, and sorting works for homogeneous lists of comparable elements.