Python_16_Udacity_Evans_Intro to CS_1_How to get started

总目录

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课程页面：https://www.udacity.com/course/intro-to-computer-science--cs101
授课教师：Dave Evans https://www.cs.virginia.edu/~evans/
如下内容包含课程笔记和自己的扩展折腾

课堂笔记

String index out of range?

• s='cs'
• 如果print s[3]会出现error string index out of range
• 但是如果是print s[3:] 就不会，只会出来empty string
• a tricky one: 如果s = "", 那么print s[0] 结果是error！

Find strings in strings

• 格式1：.find(target string)
• if target string is not found: returns -1
• 例子

s = "Von Neumann was born Neumann János Lajos \
(in Hungarian the family name comes first), \
Hebrew name Yonah, in Budapest, Kingdom of Hungary, \
which was then part of the Austro-Hungarian Empire, \
to wealthy Jewish parents of the Haskalah." 
#source: https://en.wikipedia.org/wiki/John_von_Neumann

s.find("in")

Input:

print s.find("Von")
print s[0:]
print s.find("in")
print s.find("of")
print s[126:]

Output:

0
Von Neumann was born Neumann János Lajos (in Hungarian the family name comes first), Hebrew name Yonah, in Budapest, Kingdom of Hungary, which was then part of the Austro-Hungarian Empire, to wealthy Jewish parents of the Haskalah.
43
126
of Hungary, which was then part of the Austro-Hungarian Empire, to wealthy Jewish parents of the Haskalah.

• 格式2：.find(target string, number)
• 这个number就是相当于从[number:]的地方开始找
• 但是需要注意，输出的结果还是count from the starting point of the original search string

Rounding numbers

这个练习真的很有意思

# Given a variable, x, that stores the 
# value of any decimal number, write Python 
# code that prints out the nearest whole 
# number to x.
# If x is exactly half way between two 
# whole numbers, round up, so
# 3.5 rounds to 4 and 2.5 rounds to 3.
# You may assume x is not negative.

# Hint: The str function can convert any number into a string.
# eg str(89) converts the number 89 to the string '89'

# Along with the str function, this problem can be solved 
# using just the information introduced in unit 1.

# x = 3.14159 
# >>> 3 (not 3.0)
# x = 27.63 
# >>> 28 (not 28.0)
# x = 3.5 
# >>> 4 (not 4.0)

下面是我的解答，太太太太太不美了：

x = 3.14159

#ENTER CODE BELOW HERE
xs = str(x)
point = xs.find(".")
integer_x = xs[:point]
if int(xs[point+1]) >= 5:
    print int(integer_x)+1
else:
    print int(integer_x)

正确的思路，不用round, int, if, else
极简的解法，借助数学：

x = 3.14159
x = str(x + 0.5)
point = x.find(".")
print x[:point]

太美的解法。
不过针对非大牛的人，实际编程中也不需要太注重美学，还是综合效率第一。