1. 程序要求

读取输入的字符串，是否是数字；

转换为浮点数并输出。

2. 所需方法

1）raw_input

raw_input([prompt])

2）re.match

re.match(pattern, string, flags=0)

3）类型转换

   （1）字符串转浮点

float(x) 

   （2）数字转字符串

str(x)

3. 源代码

#coding=utf-8
'''
Created on 2019年1月3日

@author: xiaobin
'''
import re
'''
#mre22_1.pl
#! /usr/bin/perl -w

# Mastering Regular Expressiona: Chapter 2 Section 2.
# first program

print "Enter a temperature in Celsius:\n";
$celsius = <STDIN>;
chomp($celsius);

if ( $celsius =~ /^[0-9]+$/) {
    $fahrenheit = ($celsius * 9 / 5) + 32;
    print "$celsius C is $fahrenheit F\n";
}
else {
    print "Expecting a number, so I don't understand \"$celsius\".\n";
}
'''
str1 = raw_input("Enter a temperature in Celsius: ")

res = re.match('^[0-9]+$', str1)

if res :
  celsius = float(str1)
  fahrenheit = (celsius * 9 / 5) + 32
  print(str1 + "C is " + str(fahrenheit) + "F")
else :
    print("Expecting a number, so I don't understand " + '\"' + str1 + '\"')

run:

Enter a temperature in Celsius: 38
38C is 100.4F

 

Reference:

1. python files io

2. search vs match

3. python numbers