SoFunction
Updated on 2024-10-29

Python Concise Beginner's Tutorials

This article is an example of a concise tutorial on getting started with Python. Shared for your reference. Specifically as follows:

I. Basic concepts

1. Number

There are 4 types of numbers in Python - integers, long integers, floating point numbers and complex numbers.
(1) 2 is an example of an integer.
(2) Long integers are nothing more than larger integers.
(2) 3.23 and 52.3E-4 are examples of floating-point numbers. the E notation denotes a power of 10. Here, 52.3E-4 represents 52.3 * 10-4.
(4) (-5 + 4j) and (2.3 - 4.6j) are examples of complex numbers.

2. String

(1) Use of single quotation marks (')
(2) Use of double quotation marks (")
(3) Use of triple quotation marks (''' or """)
With triple quotes, you can indicate a multi-line string. You are free to use single and double quotes in triple quotes. For example:

'''This is a multi-line string. This is the first line.
This is the second line.
"What's your name?," I asked.
He said "Bond, James Bond."
'''

(4) Escape character
(5) Natural strings
Natural strings are specified by prefixing the string with r or R. For example, r "Newlines are indicated by \n".

3. Logical and physical rows
The use of more than one logical line in a physical line requires the use of a semicolon (;) to specifically identify this usage. A physical line with only one logical line can be used without a semicolon.

II. Control flow

1、if

No curly brackets are used in the block, and a semicolon is used after the condition, corresponding to elif and else

if guess == number:
  print 'Congratulations, you guessed it.' # New block starts here
elif guess < number:
  print 'No, it is a little higher than that' # Another block
else:
  print 'No, it is a little lower than that'

2、while

Use a semicolon, which can be paired with else

while running:
  guess = int(raw_input('Enter an integer : '))
  if guess == number:
    print 'Congratulations, you guessed it.'
    running = False # this causes the while loop to stop
  elif guess < number:
    print 'No, it is a little higher than that'
  else:
    print 'No, it is a little lower than that'
else:
  print 'The while loop is over.'
  # Do anything else you want to do here

3、for
Use a semicolon with else

for i in range(1, 5):
  print i
else:
  print 'The for loop is over'

4. break and continue
Same as C

III. Functions

1. Definition and invocation

def sayHello():
  print 'Hello World!' # block belonging to the function
sayHello() # call the function

2、Function Formal Reference
C-like language

def printMax(a, b):
  if a > b:
    print a, 'is maximum'
  else:
    print b, 'is maximum'

3. Local variables
Add global to declare a global variable.

4. Default parameter values

def say(message, times = 1):
  print message * times

5. Key parameters
If a function has many arguments and you want to specify only some of them, you can assign values to these arguments by naming them - this is called a key argument - using the name (keyword) rather than the position to assign real parameters to the function. This has two advantages - one, it makes it easier to use the function because you don't have to worry about the order of the parameters. Two, assuming that the other parameters have default values, we can assign values to only those parameters we want.

def func(a, b=5, c=10):
  print 'a is', a, 'and b is', b, 'and c is', c
func(3, 7)
func(25, c=24)
func(c=50, a=100)

6、return

IV. Modules

1. Use of modules

import sys
print 'The command line arguments are:'
for i in :
  print i

If you want to enter the argv variable directly into the program (and avoid typing sys. every time you use it), you can use the from sys import argv statement

2. dir () function
The built-in dir function can be used to list module-defined identifiers. The identifiers are functions, classes and variables.

V. Data structure

1. List

shoplist = ['apple', 'mango', 'carrot', 'banana']
print 'I have', len(shoplist),'items to purchase.'
print 'These items are:', # Notice the comma at end of the line
for item in shoplist:
  print item,
print '\nI also have to buy rice.'
('rice')
print 'My shopping list is now', shoplist
print 'I will sort my list now'
()
print 'Sorted shopping list is', shoplist
print 'The first item I will buy is', shoplist[0]
olditem = shoplist[0]
del shoplist[0]
print 'I bought the', olditem
print 'My shopping list is now', shoplist

2. Tuple
Tuples are very similar to lists, except that tuples are immutable like strings, i.e. you can't modify a tuple.

zoo = ('wolf', 'elephant', 'penguin')
print 'Number of animals in the zoo is', len(zoo)
new_zoo = ('monkey', 'dolphin', zoo)
print 'Number of animals in the new zoo is', len(new_zoo)
print 'All animals in new zoo are', new_zoo
print 'Animals brought from old zoo are', new_zoo[2]
print 'Last animal brought from old zoo is', new_zoo[2][2]

Like a tree.

Tuples and Printing

age = 22
name = 'Swaroop'
print '%s is %d years old' % (name, age)
print 'Why is %s playing with that python?' % name

3. Dictionary

hash-like (computing)

ab = {    'Swaroop'  : 'swaroopch@',
       'Larry'   : 'larry@',
       'Matsumoto' : 'matz@',
       'Spammer'  : 'spammer@'
   }
print "Swaroop's address is %s" % ab['Swaroop']
# Adding a key/value pair
ab['Guido'] = 'guido@'
# Deleting a key/value pair
del ab['Spammer']
print '\nThere are %d contacts in the address-book\n' % len(ab)
for name, address in ():
  print 'Contact %s at %s' % (name, address)
if 'Guido' in ab: # OR ab.has_key('Guido')
  print "\nGuido's address is %s" % ab['Guido']

4. Sequence

Lists, tuples and strings are all sequences. The two main features of sequences are the index operator and the slice operator.

shoplist = ['apple', 'mango', 'carrot', 'banana']
# Indexing or 'Subscription' operation
print 'Item 0 is', shoplist[0]
print 'Item 1 is', shoplist[1]
print 'Item -1 is', shoplist[-1]
print 'Item -2 is', shoplist[-2]
# Slicing on a list
print 'Item 1 to 3 is', shoplist[1:3]
print 'Item 2 to end is', shoplist[2:]
print 'Item 1 to -1 is', shoplist[1:-1]
print 'Item start to end is', shoplist[:]
# Slicing on a string
name = 'swaroop'
print 'characters 1 to 3 is', name[1:3]
print 'characters 2 to end is', name[2:]
print 'characters 1 to -1 is', name[1:-1]
print 'characters start to end is', name[:]

5. Reference

When you create an object and assign it a variable, that variable simply refers to that object, not to the object itself! That is, the variable name points to the memory in your computer that stores that object. This is called a name-to-object binding.

print 'Simple Assignment'
shoplist = ['apple', 'mango', 'carrot', 'banana']
mylist = shoplist # mylist is just another name pointing to the same object!
del shoplist[0]
print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that both shoplist and mylist both print the same list without
# the 'apple' confirming that they point to the same object
print 'Copy by making a full slice'
mylist = shoplist[:] # make a copy by doing a full slice
del mylist[0] # remove first item
print 'shoplist is', shoplist
print 'mylist is', mylist
# notice that now the two lists are different

6. String

name = 'Swaroop' # This is a string object
if ('Swa'):
  print 'Yes, the string starts with "Swa"'
if 'a' in name:
  print 'Yes, it contains the string "a"'
if ('war') != -1:
  print 'Yes, it contains the string "war"'
delimiter = '_*_'
mylist = ['Brazil', 'Russia', 'India', 'China']
print (mylist)  // use delimiter to concatenate mylist characters

VI. Object-oriented programming

1、self

Self in Python is equivalent to the self pointer in C++ and the this reference in Java and C#.

2、Create class

class Person:
  pass # An empty block
p = Person()
print p

3. Methods of objects

class Person:
  def sayHi(self):
    print 'Hello, how are you?'
p = Person()
()

4. Initialization

class Person:
  def __init__(self, name):
     = name
  def sayHi(self):
    print 'Hello, my name is', 
p = Person('Swaroop')
()

5. Class and object methods

Class variables are shared for use by all objects (instances) of a class. There is only one copy of a class variable, so when an object makes a change to a class variable, that change is reflected on all other instances.
Object's variables are owned by each object/instance of the class. Thus each object has its own copy of this domain, i.e. they are not shared, and in different instances of the same class the variables of an object are unrelated to each other, although they have the same name.

class Person:
  '''Represents a person.'''
  population = 0
  def __init__(self, name):
    '''Initializes the person's data.'''
     = name
    print '(Initializing %s)' % 
    # When this person is created, he/she
    # adds to the population
     += 1

population belongs to the Person class and is therefore a class variable. the name variable belongs to the object (it is assigned using self) and is therefore an object variable.

6. Succession

class SchoolMember:
  '''Represents any school member.'''
  def __init__(self, name, age):
     = name
class Teacher(SchoolMember):
  '''Represents a teacher.'''
  def __init__(self, name, age, salary):
    SchoolMember.__init__(self, name, age)
     = salary

VII. Inputs and outputs

1. Documentation

f = file('', 'w') # open for 'w'riting
(poem) # write text to file
() # close the file
f = file('')
# if no mode is specified, 'r'ead mode is assumed by default
while True:
  line = ()
  if len(line) == 0: # Zero length indicates EOF
    break
  print line,
  # Notice comma to avoid automatic newline added by Python
() # close the file

2. Memory

durability

import cPickle as p
#import pickle as p
shoplistfile = ''
# the name of the file where we will store the object
shoplist = ['apple', 'mango', 'carrot']
# Write to the file
f = file(shoplistfile, 'w')
(shoplist, f) # dump the object to a file
()
del shoplist # remove the shoplist
# Read back from the storage
f = file(shoplistfile)
storedlist = (f)
print storedlist

3. Console input

Input string nID = raw_input("Input your id plz")
Input integer nAge = int(raw_input("input your age plz:\n"))
Input Floating Point fWeight = float(raw_input("input your weight\n"))
Input hex data nHex = int(raw_input('input hex value(like 0x20):\n'),16)
Input octal data nOct = int(raw_input('input oct value(like 020):\n'),8)

VIII. Exceptions

1、try..except

import sys
try:
  s = raw_input('Enter something --> ')
except EOFError:
  print '\nWhy did you do an EOF on me?'
  () # exit the program
except:
  print '\nSome error/exception occurred.'
  # here, we are not exiting the program
print 'Done'

2、Triggering abnormalities

Use the raise statement to raise the exception. You must also specify the name of the error/exception and the exception object that will accompany the exception. The error or exception you can raise should be a direct or indirect descendant of an Error or Exception class, respectively.

class ShortInputException(Exception):
  '''A user-defined exception class.'''
  def __init__(self, length, atleast):
    Exception.__init__(self)
     = length
     = atleast
raise ShortInputException(len(s), 3)

3、try..finnally

import time
try:
  f = file('')
  while True: # our usual file-reading idiom
    line = ()
    if len(line) == 0:
      break
    (2)
    print line,
finally:
  ()
  print 'Cleaning up...closed the file'

IX. Python Standard Library

1. sys library

The sys module contains the corresponding functions of the system list, which contains command line arguments.

2. os library

The string indicates the platform you are using. For example, for Windows it's 'nt' and for Linux/Unix users it's 'posix'.
() function gets the current working directory, which is the path to the directory where the current Python script is working.
The () and () functions are used to read and set environment variables, respectively.
() returns all files and directory names in the specified directory.
() function is used to delete a file.
() function is used to run shell commands.
The string gives the line terminator used by the current platform. For example, Windows uses '\r\n', Linux uses '\n' and Mac uses '\r'.
The () function returns the directory name and filename of a path.
>>> ('/home/swaroop/byte/code/')
('/home/swaroop/byte/code', '')
The () and () functions test whether the given path is a file or a directory, respectively. Similarly, the () function is used to check whether the given path really exists.

I hope that what I have described in this article will help you in your Python programming.