Python新手必备练习4---开发一个计算器程序
总是有朋友问我，在听我讲的课时感觉都能听懂，我讲的例子照着写也能做出来，但一到自己想不照抄而是自己写的时候，就发现完全没有思路，不知如何下手。对此我只能说，还是因为练习的少，平常从来不写代码，学了点语法就想啪啪啪实现复杂的功能是不现实的，学习语言是一个循序渐近的过程，不经过几万行代码的洗礼，是很难成为一个优秀的程序员的，为了帮助初学者找一些好的练习基本功的例子，我近期会整理我讲课一来的一些Python练习程序分享给大家，想学好Python的同学可以照着例子一一去做，我敢保证，把我列出的练习程序列表都做完了，你基本上就能做一个合格的Pythoner啦！
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今天做列一个题目是：开发一个简单的计算器
功能需求：
用户输入 1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )等类似公式后，必须自己解析里面的(),+,-,*,/符号和公式，运算后得出结果，结果必须与真实的计算器所得出的结果一致。
实现加减乘除
满足优先级
所需知识点：
流程控制
函数
函数递归
正则表达式
常用数据类型列表的操作
答案示例：
同学们请一定先自己做，不要看我下面的代码，自己憋出来或实在憋不出来的时候再来对比。
代码逻辑：
详细代码：
为了方便同学们明白整个逻辑过程，代码中的好多调试信息没有去掉。
#_*_coding:utf-8_*_
__author__ = 'jieli'
import re
import sys
def remove_space(data_list):
'''去除列表中的空格元素'''
for i in data_list:
if type(i) is not int:
if len(i.strip()) == 0:
data_list.remove(i)
return data_list
def fetch_data_from_bracket(data_list,first_right_bracket_pos):
'''用递归的形式取出每一对括号里的数据并进行运算且得出结果'''
print 'data list:',data_list
left_bracket_pos,right_bracket_pos = data_list.index('('),data_list.index(')') +1
print '\033[31;1mleft bracket pos:%s right_bracket_pos: %s\033[0m' %(left_bracket_pos,first_right_bracket_pos)
data_after_strip = data_list[left_bracket_pos:right_bracket_pos]
if data_after_strip.count("(") > 1:
print 'fetch_data_from_bracket:%s \033[31;1m%s\033[0m left pos:%s' %(data_after_strip,data_after_strip[1:] , left_bracket_pos)
#return fetch_data_from_bracket(data_after_strip[left_bracket_pos+1:],first_right_bracket_pos)
return fetch_data_from_bracket(data_after_strip[1:],first_right_bracket_pos)
else:
print 'last:',len(data_after_strip),data_after_strip
bracket_start_pos = first_right_bracket_pos - len(data_after_strip) +1 # (takes two position
calc_res = parse_operator(data_after_strip)
return calc_res, bracket_start_pos,first_right_bracket_pos +1 #') takes one position'
def parse_bracket(formula): #解析空格中的公式
'''解析空格中的公式，并运算出结果'''
pattern = r"\(.+\)"
m = re.search(pattern,formula) #匹配出所有的括号 ‘3 / 1 - 2 * ( (60-30 * (4-2)) - 4*3/ (6-3*2) )’ 匹配完之后是'( (60-30 * (4-2)) - 4*3/ (6-3*2) )'
if m:
data_with_brackets = m.group()
#print list(data_with_brackets)
data_with_brackets = remove_space(list(data_with_brackets))
#print data_with_brackets
calc_res = fetch_data_from_bracket(data_with_brackets,data_with_brackets.index(')'))
print '\033[32;1mResult:\033[0m', calc_res
print calc_res[1],calc_res[2]
print data_with_brackets[calc_res[1]:calc_res[2]]
del data_with_brackets[calc_res[1]:calc_res[2]]
data_with_brackets.insert(calc_res[1], str(calc_res[0])) #replace formula string with caculation result 4
return parse_bracket(''.join(data_with_brackets)) #继续处理其它的括号
else: #no bracket in formula anymore
print '\033[42;1mCaculation result:\033[0m' ,formula
def caculate_1(formula): # for multiplication and division
result = int(formula[0]) # e.g ['4', '/', '2', '*', '5'], loop start from '/'
last_operator = None
formula = list(formula)
nagative_mark = False
for index,i in enumerate(formula[1:]):
if i.isdigit():
if nagative_mark:
i = int('-'+i)
nagative_mark = False
else:
i = int(i)
#print '+++>',result,last_operator,i
if last_operator == '*':
result *= i
elif last_operator == '/':
try:
result /= i
except ZeroDivisionError,e:
print "\033[31;1mError:%s\033[0m" % e
sys.exit()
elif i == '-':
nagative_mark = True
else:
last_operator = i
print '乘除运算结果:' , result
return result
def caculate_2(data_list,operator_list):
'''eg. data_list:['4', 3, 1372, '1'] operator_list:['-', '+', '-']'''
data_list = remove_space(data_list)
print 'caculater_2:',data_list,operator_list
result = int(data_list[0])
for i in data_list[1:]:
if operator_list[0] == '+':
result += int(i)
elif operator_list[0] == '-':
result -= int(i)
del operator_list[0]
print 'caculate_2 result:', result
return result
def parse_operator(formula):
print '开始运算公式:',formula
formula = formula[1:-1] #remove bracket
low_priorities = re.findall('[+,-]',''.join(formula))
data_after_removed_low_priorities = re.split('[+,-]', ''.join(formula))
print '去掉加减后的公式列表,先算乘除:',data_after_removed_low_priorities
for index,i in enumerate(data_after_removed_low_priorities):
if i.endswith("*") or i.endswith("/") :
data_after_removed_low_priorities[index] += '-' + data_after_removed_low_priorities[index+1]
del data_after_removed_low_priorities[index+1]
print '---------->handle nagative num:',data_after_removed_low_priorities
#计算乘除运算
nagative_mark = False
for index,i in enumerate(data_after_removed_low_priorities):
if not i.isdigit():
if len(i.strip()) == 0:
nagative_mark = True
else:#remove space
string_to_list = []
if nagative_mark:
prior_l = '-' + i[0] #
nagative_mark = False
else:
prior_l = i[0]
for l in i[1:] :
if l.isdigit():
if prior_l.isdigit() or len(prior_l) >1: # two letter should be combined
prior_l += l
else:
prior_l = l
else: # an operator * or /
string_to_list.append(prior_l)
string_to_list.append(l)
prior_l = l #reset prior_l
else:
string_to_list.append(prior_l)
print '--->::', string_to_list
calc_res = caculate_1(string_to_list) #乘除运算结果
data_after_removed_low_priorities[index] = calc_res
#print '--->string to list:',string_to_list
#print '+>',index, re.split('[*,/]',i)
'''operators = re.findall('[*,/]',i)
data = re.split('[*,/]',i)
combine_to_one_list = map(None,data,operators)
combine_to_one_list =re.split("[\[,\],\(,),'',None]", str(combine_to_one_list))
combine_to_one_list = ''.join(combine_to_one_list).split()
print '-->',combine_to_one_list
#print operators,data'''
#caculate_1(combine_to_one_list)
else :
if nagative_mark:
data_after_removed_low_priorities[index] = '-' + i
print '去掉* 和 /后开始运算加减:', data_after_removed_low_priorities,low_priorities
#计算加减运算
return caculate_2(data_after_removed_low_priorities,low_priorities)
#print formula
def main():
while True:
user_input = raw_input(">>>:").strip()
if len(user_input) == 0:continue
#parse_bracket(user_input)
user_input = '(' + user_input + ')'
#parse_bracket(' 1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) ) ')
parse_bracket(user_input)
print '\033[43;1mpython计算器运算结果:\033[0m',eval(user_input)
if __name__ == '__main__':
main()