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21-while-break
break ends the loop, and the code inside the loop will not execute after break.
while True:
yn = input('Continue(y/n): ')
if yn in ['n', 'N']:
break
print('running...')
22-while-continue
Calculate the sum of even numbers within 100.
continue skips the remaining part of the current loop and goes back to the loop condition.
sum100 = 0
counter = 0
while counter < 100:
counter += 1
# if counter % 2:
if counter % 2 == 1:
continue
sum100 += counter
print(sum100)
23-for Loop Traversal of Data Objects
astr = 'hello'
alist = [10, 20, 30]
atuple = ('bob', 'tom', 'alice')
adict = {'name': 'john', 'age': 23}
for ch in astr:
print(ch)
for i in alist:
print(i)
for name in atuple:
print(name)
for key in adict:
print('%s: %s' % (key, adict[key]))
24-range Usage and Number Accumulation
# range(10) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# >>> list(range(10))
# range(6, 11) # [6, 7, 8, 9, 10]
# range(1, 10, 2) # [1, 3, 5, 7, 9]
# range(10, 0, -1) # [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
sum100 = 0
for i in range(1, 101):
sum100 += i
print(sum100)
25-List Implementation of Fibonacci Sequence
Start with two numbers in the list, and each subsequent number is the sum of the previous two.
fib = [0, 1]
for i in range(8):
fib.append(fib[-1] + fib[-2])
print(fib)
26-Multiplication Table
for i in range(1, 10):
for j in range(1, i + 1):
print('%s*%s=%s' % (j, i, i * j), end=' ')
print()
# i=1 ->j: [1]
# i=2 ->j: [1,2]
# i=3 ->j: [1,2,3]
# Specified by the user up to which number to multiply
n = int(input('number: '))
for i in range(1, n + 1):
for j in range(1, i + 1):
print('%s*%s=%s' % (j, i, i * j), end=' ')
print()
27-Step-by-Step List Comprehension
# Store the result of 10+5 in a list
[10 + 5]
# The expression 10+5 is calculated 10 times
[10 + 5 for i in range(10)]
# 10+i where i comes from the loop
[10 + i for i in range(10)]
[10 + i for i in range(1, 11)]
# Filter with if, only those that meet the if condition participate in the calculation of 10+i
[10 + i for i in range(1, 11) if i % 2 == 1]
[10 + i for i in range(1, 11) if i % 2]
# Generate a list of IP addresses
['192.168.1.%s' % i for i in range(1, 255)]
28-Best of Three Rock-Paper-Scissors
import random
all_choices = ['Rock', 'Scissors', 'Paper']
win_list = [['Rock', 'Scissors'], ['Scissors', 'Paper'], ['Paper', 'Rock']]
prompt = """(0) Rock
(1) Scissors
(2) Paper
Please choose (0/1/2): """
cwin = 0
pwin = 0
while cwin < 2 and pwin < 2:
computer = random.choice(all_choices)
ind = int(input(prompt))
player = all_choices[ind]
print("Your choice: %s, Computer's choice: %s" % (player, computer))
if player == computer:
print('\033[32;1m Draw, \033[0m')
elif [player, computer] in win_list:
pwin += 1
print('\033[31;1mYou WIN!!!\033[0m')
else:
cwin += 1
print('\033[31;1mYou LOSE!!!\033[0m')
29-Basic File Object Operations
# The three steps of file operations: open, read/write, close
# cp /etc/passwd /tmp
f = open('/tmp/passwd') # Open text file in read mode by default
data = f.read() # read() reads all contents
print(data)
data = f.read() # As reading and writing proceed, the file pointer moves forward.
# Because the first f.read() has already moved the file pointer to the end, reading again yields no data
# So data is an empty string
f.close()
f = open('/tmp/passwd')
data = f.read(4) # Read 4 bytes
f.readline() # Read until newline, ends at n
f.readlines() # Read each line of data into a list
f.close()
################################
f = open('/tmp/passwd')
for line in f:
print(line, end='')
f.close()
##############################
f = open('image_path', 'rb') # Open non-text file with b parameter
f.read(4096)
f.close()
##################################
f = open('/tmp/myfile', 'w') # Open file in 'w' mode, creates if not exist
f.write('hello world!\n')
f.flush() # Immediately sync cached data to disk
f.writelines(['2nd line.\n', 'new line.\n'])
f.close() # Save data to disk when closing the file
##############################
with open('/tmp/passwd') as f:
print(f.readline())
#########################
f = open('/tmp/passwd')
f.tell() # Check the position of the file pointer
f.readline()
f.tell()
f.seek(0, 0) # The first number is the offset, the 2nd is the relative position.
# Relative position 0 means start, 1 means current, 2 means end
f.tell()
f.close()
30-Copying Files
Copying files means opening the source file in r mode, opening the target file in w mode, reading data from the source file, and writing it to the target file.
The following is a [not recommended] method, but it works:
f1 = open('/bin/ls', 'rb')
f2 = open('/root/ls', 'wb')
data = f1.read()
f2.write(data)
f1.close()
f2.close()
31-Copying Files
Read 4K each time, until finished:
src_fname = '/bin/ls'
dst_fname = '/root/ls'
src_fobj = open(src_fname, 'rb')
dst_fobj = open(dst_fname, 'wb')
while True:
data = src_fobj.read(4096) # Read 4K each time
if not data:
break
dst_fobj.write(data)
src_fobj.close()
dst_fobj.close()
32-Position Parameters
Note: The numbers in position parameters are in string form
import sys
print(sys.argv) # sys.argv is the argv list in the sys module
# python3 position_args.py
# python3 position_args.py 10
# python3 position_args.py 10 bob
33-Function Application – Fibonacci Sequence
def gen_fib(l):
fib = [0, 1]
for i in range(l - len(fib)):
fib.append(fib[-1] + fib[-2])
return fib # Return list, not variable fib
a = gen_fib(10)
print(a)
print('-' * 50)
n = int(input("length: "))
print(gen_fib(n)) # n is assigned to parameter, not passed as variable n
34-Function – Copy Files
import sys
def copy(src_fname, dst_fname):
src_fobj = open(src_fname, 'rb')
dst_fobj = open(dst_fname, 'wb')
while True:
data = src_fobj.read(4096)
if not data:
break
dst_fobj.write(data)
src_fobj.close()
dst_fobj.close()
copy(sys.argv[1], sys.argv[2])
# Execution method
# cp_func.py /etc/hosts /tmp/zhuji.txt
35-Function – Multiplication Table
def mtable(n):
for i in range(1, n + 1):
for j in range(1, i + 1):
print('%s*%s=%s' % (j, i, i * j), end=' ')
print()
mtable(6)
mtable(9)
36-Module Basics
Every file with a .py extension is a module.
star.py：
hi = 'hello world!'
def pstar(n=50):
print('*' * n)
if __name__ == '__main__':
pstar()
pstar(30)
To call the star module in call_star.py:
import star
print(star.hi)
star.pstar()
star.pstar(30)
37-Generate Password/Verification Code
This file is named: randpass.py
Idea:
1. Set a base string for randomly selecting characters, using uppercase and lowercase letters plus digits in this example
2. Loop n times, randomly select a character each time
3. Concatenate the characters and save to the variable result
from random import choice
import string
all_chs = string.ascii_letters + string.digits # Uppercase and lowercase letters plus digits
def gen_pass(n=8):
result = ''
for i in range(n):
ch = choice(all_chs)
result += ch
return result
if __name__ == '__main__':
print(gen_pass())
print(gen_pass(4))
print(gen_pass(10))
38-Sequence Object Methods
from random import randint
alist = list() # []
list('hello') # ['h', 'e', 'l', 'l', 'o']
list((10, 20, 30)) # [10, 20, 30] Convert tuple to list
astr = str() # ''
str(10) # '10'
str(['h', 'e', 'l', 'l', 'o']) # Convert list to string
atuple = tuple() # ()
tuple('hello') # ('h', 'e', 'l', 'l', 'o')
num_list = [randint(1, 100) for i in range(10)]
max(num_list)
min(num_list)
39-Sequence Object Methods 2
alist = [10, 'john']
# list(enumerate(alist)) # [(0, 10), (1, 'john')]
# a, b = 0, 10 # a->0 ->10
for ind in range(len(alist)):
print('%s: %s' % (ind, alist[ind]))
for item in enumerate(alist):
print('%s: %s' % (item[0], item[1]))
for ind, val in enumerate(alist):
print('%s: %s' % (ind, val))
atuple = (96, 97, 40, 75, 58, 34, 69, 29, 66, 90)
sorted(atuple)
sorted('hello')
for i in reversed(atuple):
print(i, end=',')
40-String Methods
py_str = 'hello world!'
py_str.capitalize()
py_str.title()
py_str.center(50)
py_str.center(50, '#')
py_str.ljust(50, '*')
py_str.rjust(50, '*')
py_str.count('l') # Count occurrences of l
py_str.count('lo')
py_str.endswith('!') # Ends with !?
py_str.endswith('d!')
py_str.startswith('a') # Starts with a?
py_str.islower() # Are all letters lowercase? Ignore other characters
py_str.isupper() # Are all letters uppercase? Ignore other characters
'Hao123'.isdigit() # Are all characters digits?
'Hao123'.isalnum() # Are all characters alphanumeric?
' hello\t '.strip() # Remove whitespace from both ends, commonly used
' hello\t '.lstrip()
' hello\t '.rstrip()
'how are you?'.split()
'hello.tar.gz'.split('.')
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