Learning in Python：Chapter 4 Introducing Python Object Types

Chapter 4: Introducing Python Object Types

 

 

1. Build-in Types:

 

        

 

2. Numbers:

• Python support big numbers
• Modules: math, random

3. String:

• String is a Sequence
• Sequence operation:
• len(s)
• s[1], s[-1]
• s[1:3], s[:3], s[1:], s[:-1]
• s + 'abc'
• s*8
• Type-Specific methods:
• s.find('abc')
• s.replace('abc','bbb')
• s.split(',')
• s.upper()
• s.isalpha(), s.isdigit()
• s.rstrip()
• Formating:
• '%s hello, %s world' % ('I', 'python')
• '{0} hello, {1} world'.format('I','python')
• '{0:o}, {1:x}, {2:b}'.format(64, 64, 64)
• String is Immutable (not changing the original string, but creating new one), but can be used to make new strings.
• numbers, strings, and tuples are immutable; lists and dictionaries are not
• \0 does not teminates a string
• """  """ for mutiple-line string. r'' for raw string
• pattern matching:
• module:  re

3. Getting help

• dir(s), help(s.replace)

 

4. List

• Mutable, Sequence
• Tpye-Specific Operations:
• L.append()
• L.pop(2)    # pop out the second last item
• L.insert()
• L.remove()
• L.sort()
• L.reverse()
• Comprehension:
• [row[1] + 1 for row in M]
• [row[1] + 1 for row in M if row[1]%2 == 0]
• {ord(x) for x in 'spaam'}
• {x:ord(x) for x in 'spaam'}
• Generator
• G = ( sum(row) for row in M )
• next(G)

5. Dictinary

• Mapping (no order), mutable
• Type-specific operations:
• D.keys()
• sorted(D)  The Dictionary can be ordered.
• Iteration Protocol: a physically stored sequence in memory.
• Time optimization module: time,  timeit, profile
• Missing Key:
• if a in D
• get: value = D.get('x', 0)
• if/else expression: value = D['x'] if 'x' in D else 0

6. Tuples

• A list that cannot be changed: immutable
• Type-specific methods:
• T.index(4)   return the index of 4
• T.count(4)   return the exsit times of 4

7. Files

• file = open("abc.txt","w")
• w: clear/create a file for writing
• file.write()
• Read:
• file.read(), read the entire file
• file.readline(), read one line at a time
• file.seek()

8.set

• X = set('spam')
• Y = {'h', 'a', 'm'}
• >>> X, Y
• >>> X & Y # Intersection
• >>> X | Y # Union
• >>> X – Y # Difference
• >>> {x ** 2 for x in [1, 2, 3, 4]} # Set comprehensions in 3.0

9.  type build-in function

• type()    return the type of a object
• isinstance(L, list)