Click the image below to search for the secret code[Interview Guide], claim it nowInterview Questions + Resume Template.
41 – String Formatting
"%s is %s years old" % ('bob', 23) # Commonly used
"%s is %d years old" % ('bob', 23) # Commonly used
"%s is %d years old" % ('bob', 23.5) # %d is an integer, commonly used
"%s is %f years old" % ('bob', 23.5)
"%s is %5.2f years old" % ('bob', 23.5) # %5.2f has a width of 5 and 2 decimal places
"97 is %c" % 97
"11 is %#o" % 11 # %#o indicates octal with prefix
"11 is %#x" % 11
"%10s%5s" % ('name', 'age') # %10s indicates a total width of 10, right-aligned, commonly used
"%10s%5s" % ('bob', 25)
"%10s%5s" % ('alice', 23)
"%-10s%-5s" % ('name', 'age') # %-10s indicates left alignment, commonly used
"%-10s%-5s" % ('bob', 25)
"%10d" % 123
"%010d" % 123
"{} is {} years old".format('bob', 25)
"{1} is {0} years old".format(25, 'bob')
"{:<10}{:<8}".format('name', 'age')
42 – Common Methods of shutil Module
import shutil
with open('/etc/passwd', 'rb') as sfobj:
with open('/tmp/mima.txt', 'wb') as dfobj:
shutil.copyfileobj(sfobj, dfobj) # Copy file object
shutil.copyfile('/etc/passwd', '/tmp/mima2.txt')
shutil.copy('/etc/shadow', '/tmp/') # cp /etc/shadow /tmp/
shutil.copy2('/etc/shadow', '/tmp/') # cp -p /etc/shadow /tmp/
shutil.move('/tmp/mima.txt', '/var/tmp/') # mv /tmp/mima.txt /var/tmp/
shutil.copytree('/etc/security', '/tmp/anquan') # cp -r /etc/security /tmp/anquan
shutil.rmtree('/tmp/anquan') # rm -rf /tmp/anquan
# Set permissions of mima2.txt to be the same as /etc/shadow
shutil.copymode('/etc/shadow', '/tmp/mima2.txt')
# Set metadata of mima2.txt to be the same as /etc/shadow
# Use stat /etc/shadow to view metadata
shutil.copystat('/etc/shadow', '/tmp/mima2.txt')
shutil.chown('/tmp/mima2.txt', user='zhangsan', group='zhangsan')
43 – Exercise: Generate Text File
import os
def get_fname():
while True:
fname = input('filename: ')
if not os.path.exists(fname):
break
print('%s already exists. Try again' % fname)
return fname
def get_content():
content = []
print('Input data, type end to finish')
while True:
line = input('> ')
if line == 'end':
break
content.append(line)
return content
def wfile(fname, content):
with open(fname, 'w') as fobj:
fobj.writelines(content)
if __name__ == '__main__':
fname = get_fname()
content = get_content()
content = ['%s\n' % line for line in content]
wfile(fname, content)
44 – List Methods
alist = [1, 2, 3, 'bob', 'alice']
alist[0] = 10
alist[1:3] = [20, 30]
alist[2:2] = [22, 24, 26, 28]
alist.append(100)
alist.remove(24) # Delete the first 24
alist.index('bob') # Return index
blist = alist.copy() # Equivalent to blist = alist[:]
alist.insert(1, 15) # Insert number 15 at index 1
alist.pop() # Default pops the last item
alist.pop(2) # Pops the item at index 2
alist.pop(alist.index('bob'))
alist.sort()
alist.reverse()
alist.count(20) # Count occurrences of 20 in the list
alist.clear() # Clear the list
alist.append('new')
alist.extend('new')
alist.extend(['hello', 'world', 'hehe'])
45 – Check Valid Identifier
import sys
import keyword
import string
first_chs = string.ascii_letters + '_'
all_chs = first_chs + string.digits
def check_id(idt):
if keyword.iskeyword(idt):
return "%s is keyword" % idt
if idt[0] not in first_chs:
return "1st invalid"
for ind, ch in enumerate(idt[1:]):
if ch not in all_chs:
return "char in position #%s invalid" % (ind + 2)
return "%s is valid" % idt
if __name__ == '__main__':
print(check_id(sys.argv[1])) # python3 checkid.py abc@123
46 – Create User and Set Random Password
Refer to the randpass module in "37 - Generate Password/Verification Code"
import subprocess
import sys
from randpass import gen_pass
def adduser(username, password, fname):
data = """user information:
%s: %s
"""
subprocess.call('useradd %s' % username, shell=True)
subprocess.call(
'echo %s | passwd --stdin %s' % (password, username),
shell=True
)
with open(fname, 'a') as fobj:
fobj.write(data % (username, password))
if __name__ == '__main__':
username = sys.argv[1]
password = gen_pass()
adduser(username, password, '/tmp/user.txt')
# python3 adduser.py john
47 – List Exercise: Simulate Stack Operations
stack = []
def push_it():
item = input('item to push: ')
stack.append(item)
def pop_it():
if stack:
print("from stack popped %s" % stack.pop())
def view_it():
print(stack)
def show_menu():
cmds = {'0': push_it, '1': pop_it, '2': view_it} # Store functions in a dictionary
prompt = """(0) push it
(1) pop it
(2) view it
(3) exit
Please input your choice(0/1/2/3): """
while True:
# input() gets a string, use strip() to remove whitespace, then take the first character
choice = input(prompt).strip()[0]
if choice not in '0123':
print('Invalid input. Try again.')
continue
if choice == '3':
break
cmds[choice]()
if __name__ == '__main__':
show_menu()
48 – Implement Unix2Dos Functionality in Linux
import sys
def unix2dos(fname):
dst_fname = fname + '.txt'
with open(fname) as src_fobj:
with open(dst_fname, 'w') as dst_fobj:
for line in src_fobj:
line = line.rstrip() + '\r\n'
dst_fobj.write(line)
if __name__ == '__main__':
unix2dos(sys.argv[1])
49 – Animation Program: @ Moving Through a Line of #
\r is carriage return without line break
import time
length = 19
count = 0
while True:
print('\r%s@%s' % ('#' * count, '#' * (length - count)), end='')
try:
time.sleep(0.3)
except KeyboardInterrupt:
print('\nBye-bye')
break
if count == length:
count = 0
count += 1
50 – Basic Dictionary Usage
adict = dict() # {}
dict(['ab', 'cd'])
bdict = dict([('name', 'bob'),('age', 25)])
{}.fromkeys(['zhangsan', 'lisi', 'wangwu'], 11)
for key in bdict:
print('%s: %s' % (key, bdict[key]))
print("%(name)s: %(age)s" % bdict)
bdict['name'] = 'tom'
bdict['email'] = '[email protected]'
del bdict['email']
bdict.pop('age')
bdict.clear()
51 – Common Dictionary Methods
adict = dict([('name', 'bob'),('age', 25)])
len(adict)
hash(10) # Check if the given data is immutable, only immutable data can be used as key
adict.keys()
adict.values()
adict.items()
# get method is commonly used, important
adict.get('name') # Get the value corresponding to name in the dictionary, returns None if not found
print(adict.get('qq')) # None
print(adict.get('qq', 'not found')) # If qq is not found, return specified content
print(adict.get('age', 'not found'))
adict.update({'phone': '13455667788'})
52 – Common Set Methods
# A set is essentially a dictionary with no values, so it is also represented by {}
myset = set('hello')
len(myset)
for ch in myset:
print(ch)
aset = set('abc')
bset = set('cde')
aset & bset # Intersection
aset.intersection(bset) # Intersection
aset | bset # Union
aset.union(bset) # Union
aset - bset # Difference
aset.difference(bset) # Difference
aset.add('new')
aset.update(['aaa', 'bbb'])
aset.remove('bbb')
cset = set('abcde')
dset = set('bcd')
cset.issuperset(dset) # Is cset a superset of dset?
cset.issubset(dset) # Is cset a subset of dset?
53 – Set Example: Extract Lines Present in the Second File but Not in the First
# cp /etc/passwd .
# cp /etc/passwd mima
# vim mima -> Modify, differing from passwd
with open('passwd') as fobj:
aset = set(fobj)
with open('mima') as fobj:
bset = set(fobj)
with open('diff.txt', 'w') as fobj:
fobj.writelines(bset - aset)
54 – Dictionary Exercise: Simulate Registration/Login
import getpass
userdb = {}
def register():
username = input('username: ')
if username in userdb:
print('%s already exists.' % username)
else:
password = input('password: ')
userdb[username] = password
def login():
username = input('username: ')
password = getpass.getpass("password: ")
if userdb.get(username) != password:
print('login failed')
else:
print('login successful')
def show_menu():
cmds = {'0': register, '1': login}
prompt = """(0) register
(1) login
(2) exit
Please input your choice(0/1/2): """
while True:
choice = input(prompt).strip()[0]
if choice not in '012':
print('Invalid input. Try again.')
continue
if choice == '2':
break
cmds[choice]()
if __name__ == '__main__':
show_menu()
55 – Calculate Time for Ten Million Addition Operations
import time
result = 0
start = time.time() # Return timestamp before operation
for i in range(10000000):
result += i
end = time.time() # Return timestamp after operation
print(result)
print(end - start)
56 – Common Methods of Time Related Modules
import time
t = time.localtime() # Return current time as a tuple
time.gmtime() # Return current time in Greenwich Mean Time as a tuple
time.time() # Commonly used, seconds since 1970-1-1 8:00, timestamp
time.mktime(t) # Convert tuple time to timestamp
time.sleep(1)
time.asctime() # If there are parameters, it is in tuple form
time.ctime() # Return current time, parameter is timestamp, commonly used
time.strftime("%Y-%m-%d") # Commonly used
time.strptime('2018-07-20', "%Y-%m-%d") # Return tuple time format
time.strftime('%H:%M:%S')
###########################################
from datetime import datetime
from datetime import timedelta
datetime.today() # Return current time as a datetime object
datetime.now() # Same as above, can use timezone as parameter
datetime.strptime('2018/06/30', '%Y/%m/%d') # Return datetime object
dt = datetime.today()
datetime.ctime(dt)
datetime.strftime(dt, "%Y%m%d")
days = timedelta(days=90, hours=3) # Commonly used
dt2 = dt + days
dt2.year
dt2.month
dt2.day
dt2.hour
57 – Common Methods of os Module
import os
os.getcwd() # Show current path
os.listdir() # ls -a
os.listdir('/tmp') # ls -a /tmp
os.mkdir('/tmp/mydemo') # mkdir /tmp/mydemo
os.chdir('/tmp/mydemo') # cd /tmp/mydemo
os.listdir()
os.mknod('test.txt') # touch test.txt
os.symlink('/etc/hosts', 'zhuji') # ln -s /etc/hosts zhuji
os.path.isfile('test.txt') # Check if test.txt is a file
os.path.islink('zhuji') # Check if zhuji is a symlink
os.path.isdir('/etc')
os.path.exists('/tmp') # Check if it exists
os.path.basename('/tmp/abc/aaa.txt')
os.path.dirname('/tmp/abc/aaa.txt')
os.path.split('/tmp/abc/aaa.txt')
os.path.join('/home/tom', 'xyz.txt')
os.path.abspath('test.txt') # Return absolute path of test.txt in current directory
58 – Pickle Storage
import pickle
"""Previous file writing could only write strings. If you want to write any data object (numbers, lists, etc.) to a file,
use pickle to ensure data type remains unchanged when retrieved"""
# shop_list = ["eggs", "apple", "peach"]
# with open('/tmp/shop.data', 'wb') as fobj:
# pickle.dump(shop_list, fobj)
with open('/tmp/shop.data', 'rb') as fobj:
mylist = pickle.load(fobj)
print(mylist[0], mylist[1], mylist[2])
59 – Basic Exception Handling
try: # Put statements that may raise exceptions in try block
n = int(input("number: "))
result = 100 / n
print(result)
except ValueError:
print('invalid number')
except ZeroDivisionError:
print('0 not allowed')
except KeyboardInterrupt:
print('Bye-bye')
except EOFError:
print('Bye-bye')
print('Done')
60 – Complete Syntax of Exception Handling
try:
n = int(input("number: "))
result = 100 / n
except (ValueError, ZeroDivisionError):
print('invalid number')
except (KeyboardInterrupt, EOFError):
print('\nBye-bye')
else:
print(result) # Executes only if no exceptions occur
finally:
print('Done') # Statements that must execute regardless of whether an exception occurs
# Common forms include try-except and try-finally
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