Day - for 循环和索引

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查找斐波那契数列：

生成达到给定数字的斐波那契数列。
示例：输入：10 → 输出：0, 1, 1, 2, 3, 5, 8.

f, s = -1, 1
t = 0
while t<=13:
    t= f + s
    print(t,end= ' ')
    f,s = s, t

0 1 1 2 3 5 8 13 21 

不使用第三个变量查找斐波那契数列：

f, s = -1, 1 
while f+s<=13: 
    print(f + s,end= ' ')  
    f,s = s, f + s

0 1 1 2 3 5 8 13 

for 循环：

for 循环是编程中使用的控制流语句，用于将代码块重复特定次数或迭代序列。

语法：

for variable in iterable:

步骤运算符：

步骤运算符是指为循环中的迭代指定增量（或步骤）的能力。在 python 中，这通常与 range() 函数一起使用，它允许指定一个步骤来控制循环变量在每次迭代后如何变化。

语法：

range(start, stop, step)

start：序列的起始值（含）。
stop：序列的停止值（不包括）。
步骤：序列在每次迭代中增加（或减少，如果为负）的量。

print("first output")
for no in range(10):
    print(no, end=' ')

print("\nsecond output")
for no in range(1,10):
    print(no, end=' ')

print("\nthird output")
for no in range(5,10):
    print(no, end=' ')

print("\nfourth output")
for no in range(1,10,2):
    print(no, end=' ')

print("\nfifth output")
for no in range(3,15,3):
    print(no, end=' ')

print("\nsixth output")
for no in range(10,1):
    print(no, end=' ')

print("\nseventh output")
for no in range(10,1,-1):
    print(no, end=' ')

print("\neighth output")
for no in range(20,3,-1):
    print(no, end=' ')

print("\nnineth output")
for no in range(20,2,-2):
    print(no, end=' ')

first output
0 1 2 3 4 5 6 7 8 9 
second output
1 2 3 4 5 6 7 8 9 
third output
5 6 7 8 9 
fourth output
1 3 5 7 9 
fifth output
3 6 9 12 
sixth output

seventh output
10 9 8 7 6 5 4 3 2 
eighth output
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 
nineth output
20 18 16 14 12 10 8 6 4

索引：

索引是指使用元素的位置或索引来访问序列（如列表、元组或字符串）中的元素。

索引类型：

1.正索引：
第一个元素从 0 开始。

2.负索引：
最后一个元素从 -1 开始。

name = 'abcdefghi'
print("first output")
for letter in name[0:5]:  
    print(letter, end=' ')
print("\nsecond output")
for letter in name[0:6:2]:
    print(letter, end=' ')
print("\nthird output")
for letter in name[8:0:-1]:
    print(letter, end=' ')
print("\nfourth output")
for letter in name[8:2:-1]:
    print(letter, end=' ')
print("\nfifth output")
for letter in name[8:-1:-1]:
    print(letter, end=' ')
print("\nsixth output")
for letter in name[8:3:-2]:
    print(letter, end=' ')
print("\nseventh output")
for letter in name[8::-1]:
    print(letter, end=' ')
print("\nninth output")
for letter in name[::]:
    print(letter, end=' ')
print("\ntenth output")
for letter in name[6::]:
    print(letter, end=' ')
print("\neleventh output")
for letter in name[2::2]:
    print(letter, end=' ')

first output
a b c d e 
second output
a c e 
third output
i h g f e d c b 
fourth output
i h g f e d 
fifth output

sixth output
i g e 
seventh output
i h g f e d c b a 
ninth output
a b c d e f g h i 
tenth output
g h i 
eleventh output
c e g i

name = 'abcdefghi'
print(name[0])
print(name[-1])
print(name[-2])
print(name[-3])
print(name[-1::-1])

a
i
h
g
ihgfedcba

编写一个程序来检查给定的字符串是否是回文

name = input("enter word: ")
if name[::] == name[::-1]:
    print("palindrome")
else:
    print("not palindrome")

enter word: amma
palindrome
enter word: ggfhyjdr
not palindrome

name = 'abcd'
print(name * 3)

abcdabcdabcd

name = 'abcd'
print(name + 3)

typeerror: can only concatenate str (not "int") to str

this error occurs because you're trying to concatenate a string (name) with an integer (3) using the + operator. in python, the + operator for strings is used for concatenation, but both operands must be strings.

for num in range(5):
    print("* " * num)

* 
* * 
* * * 
* * * * 

for num in range(1,6):
    print("* " * num)

* 
* * 
* * * 
* * * * 
* * * * * 

for num in range(5,0,-1):
    print("* " * num)

* * * * * 
* * * * 
* * * 
* * 
* 

digit = "1"
for num in range(5,0,-1): 
    print(digit * num)
    digit = str(int(digit)+1) 

11111
2222
333
44
5

任务：

abcdefghi
xyz
zyxwv
acegi
伊格卡
zxvtrpnljhfdb

word = 'abcdefghijklmnopqrstuvwxyz'
print("first output")
for letter in word[0:9]:
    print(letter , end=" ")
print("\nsecond output")
for letter in word[23::]:
    print(letter , end=" ")
print("\nthird output")
for letter in word[-1:-6:-1]:
    print(letter , end=" ")
print("\nfouth output")
for letter in word[0:9:2]:
    print(letter , end=" ")
print("\nfifth output")
for letter in word[8::-2]:
    print(letter , end=" ")
print("\nsixth output")
for letter in word[-1::-2]:
    print(letter , end=" ")

First Output
A B C D E F G H I 
Second Output
X Y Z 
Third Output
Z Y X W V 
Fouth Output
A C E G I 
Fifth Output
I G E C A 
Sixth Output
Z X V T R P N L J H F D B

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