Expressions and statements in Python and for and while loop exercises
- expression
Common expression operators:
x + y, x - y
x * y, x / y, x // y, x % y
Logical operation:
x or y, x and y, not x
Membership operation:
x in y, x not in y
Object instance test:
x is y, x not is y
Comparison operation:
x < y, x > y, x <= y, x >= y, x == y, x != y
Operation:
x | y, x & y, x ^ y, x << y, x >> y
1 Operation:
-x, +x, ~x:
Power operation:
x ** y
Index and sharding:
x[i], x[i:j], x[i:j:stride]
Call:
x(...)
Take attributes:
x.attribute
Tuples: (...)
Sequence: [...]
Dictionary: {...}
3 Meta selection expression: x if y else z
Anonymous function: lambda args: expression
Generator function sending protocol: yield x
Operation priority:
(...), [...], {...}
s[i], s[i:j]
s.attribute
s(...)
+x, -x, ~x
x ** y
*, /, //, %
+, -
<<, >>
&
^
|
<, <=, >, >=, ==, !=
is, not is
in, not in
not
and
or
lambda- statement:
Assignment statement
call
print : Print the object
if/elif/else: conditional
for/else: Sequence iteration
while/else: General circulation
pass: A placeholder
break:
continue
def
return
yield
global: The namespace
raise: An exception
import:
from: Module property access
class: class
try/except/finally: The catching
del: Delete the reference
assert: Debugging check
with/as: Environment manager
Assignment statement:
Implicit assignment: import, from, def, class, for, Function parameters
Tuple and list decomposition assignments: When assigning symbols (=) When the left side is a tuple or list, Python The object on the right and the target on the left are rounded from left to right by position 1 To pair; When the number is different, an exception will be triggered, which can be done in the way of slicing.
Multiple target assignments
Strengthen the assignment : +=, -=, *=, /=, //=, %=,3)for cycle exercises
practice 1 Chase: 1 Displays the specified dictionary separately d1 All elements in, like the following
k1 v1
k2 v2
...
>>> d1 = { 'x':1,'y':2,'z':3,'m':4 }
>>> for (k,v) in d1.items():
print k,v
y 2
x 1
z 3
m 4
practice 2 Chase: 1 Display list l1=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"] Element whose index is odd;
>>> l1 = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
>>> for i in range(1,len(l1),2):
print l1[i]
Mon
Wed
Fri
practice 3 : will belong to the list l1=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"] But not on the list l2=["Sun","Mon","Tue","Thu","Sat"] Is defined as 1 A new list l3;
>>> l1 = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
>>> l2 = ["Sun","Mon","Tue","Thu","Sat"]
>>> l3 = [ ]
>>> for i in l1:
if i not in l2:
l3.append(i)
>>> l3
['Wed', 'Fri']
practice 4 : Known list namelist=['stu1','stu2','stu3','stu4','stu5','stu6','stu7'] , delete the list removelist=['stu3', 'stu7', 'stu9'] ; Please will belong to removelist Each element in the list is from namelist Remove the ( Belong to removelist But not belonging to namelist Just ignore ) ;
>>> namelist= ['stu1','stu2','stu3','stu4','stu5','stu6','stu7']
>>> removelist = ['stu3', 'stu7', 'stu9']
>>> for i in namelist:
if i in removelist :
namelist.remove(i)
>>> namelist
['stu1', 'stu2', 'stu4', 'stu5', 'stu6']4)while cycle exercises
practice 1 Chase: 1 Displays all elements in the specified list;
>>> l1 = [1,2,3,4,5]
>>> i = 0
>>> while i < len(l1)
print l1[i]
i += 1
1
2
3
4
5
>>> l1 = [1,2,3,4,5]
>>> while l1:
print l1.pop(0)
1
2
3
4
5
practice 2 : o 100 The sum of all even Numbers within;
>>> i = 0
>>> sum = 0
>>> while i < 101:
sum += i
i += 2
print sum
2550
>>> for i in range(0,101,2):
sum+=i
print sum
2550
practice 3 Chase: 1 Displays all keys for the specified dictionary; And indicate the total number of keys at the end of display;
>>> d1 = {'x':1, 'y':23, 'z': 78}
>>> i1 = d1.keys()
>>> while i1:
print i1.pop(0)
else:
print len(d1)
x
y
z
3
practice 4 : create 1 A contains 100 A list of all odd Numbers within;
>>> d1 = [ ]
>>> i = 1
>>> while i < 101:
d1.append(i)
i+=2
>>> print d1
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]
>>> d1 = [ ]
>>> for i in range(1,101,2)
d1.append(i)
>>> print d1
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]
practice 5 List: l1=[0,1,2,3,4,5,6], The list of l2=["Sun","Mon","Tue","Wed","Thu","Fri","Sat"] To the first 1 The element in the list is the key to the first 2 Elements in a list generate dictionaries for values d1 ;
>>> l1 = [0,1,2,3,4,5,6]
>>> l2 = ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"]
>>> d1 = {}
>>> count = 0
>>> if len(l1) == len(l2):
while count < len(l1):
d1[l1[count]] = l2[count]
count += 1