1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Tutorial slides on Python.
%
% Author: FOSSEE
% Copyright (c) 2017, FOSSEE, IIT Bombay
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass[14pt,compress]{beamer}
\input{macros.tex}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Title page
\title[Files/exceptions]{Practice exercises: files and exceptions}
\author[FOSSEE Team] {The FOSSEE Group}
\institute[FOSSEE -- IITB] {Department of Aerospace Engineering\\IIT Bombay}
\date[] {Mumbai, India}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% DOCUMENT STARTS
\begin{document}
\begin{frame}
\titlepage
\end{frame}
\begin{frame}[plain]
\frametitle{Exercise: reading from a file}
\begin{enumerate}
\item Define a function called \typ{largest} which takes a single argument
\item The argument passed will be an opened file object
\item Read the data in the file
\item Assume that the data is separated by spaces and are all numbers
\item Find the maximum value in the file
\item Do not use \typ{loadtxt}!
\end{enumerate}
\end{frame}
\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
def largest(f):
data = []
for line in f:
for field in line.split():
data.append(float(field))
return max(data)
\end{lstlisting}
\end{frame}
\begin{frame}[fragile,plain]
\frametitle{Another solution}
\begin{lstlisting}
def largest(f):
res = -1e20
for line in f:
for field in line.split():
res = max(res, float(field))
return res
\end{lstlisting}
\end{frame}
\begin{frame}[plain]
\frametitle{Exercise: reading/writing files}
\begin{enumerate}
\item Read the \typ{pendulum.txt} file
\item Print the second column alone to another file called \typ{col2.txt}
\item Remember to add a newline
\end{enumerate}
\end{frame}
\begin{frame}[fragile,plain]
\frametitle{Solution}
\begin{lstlisting}
f = open('pendulum.txt')
out = open('col2.txt', 'w')
for line in f:
fields = line.split()
out.write(fields[1] + '\n')
f.close()
out.close()
\end{lstlisting}
\end{frame}
\begin{frame}[fragile,plain]
\frametitle{Another solution}
\begin{lstlisting}
f = open('pendulum.txt')
out = open('col2.txt', 'w')
for line in f:
fields = line.split()
print(fields[1], file=out)
f.close()
out.close()
\end{lstlisting}
\end{frame}
\begin{frame}[plain, fragile]
\frametitle{Exercise: simple exceptions}
\begin{enumerate}
\item Write a function called \typ{my\_sum}
\item The function is passed a single string with terms separated by spaces
\item The string contains both names and integer values in arbitrary order
\item Find the sum of all the numbers in the string
\end{enumerate}
For example:
\begin{lstlisting}
>>> my_sum('1 fox, 2 dogs and 3 jackals')
6
>>> my_sum('3 blind mice and 1 man')
4
\end{lstlisting}
\end{frame}
\begin{frame}[fragile,plain]
\frametitle{Possible solution}
\begin{lstlisting}
def my_sum(s):
total = 0
for word in s.split():
try:
total += int(word)
except ValueError:
pass
return total
\end{lstlisting}
\end{frame}
\begin{frame}[plain, fragile]
\frametitle{Exercise: catching exceptions}
\small
\begin{enumerate}
\item Write a function called \typ{safe\_run(f, x)}
\item \typ{f} is a function and \typ{x} is a value
\item \typ{f} can raise either \typ{ValueError} or \typ{TypeError}
\item Your function should return \typ{'OK'} if no exception is raised
\item Return \typ{'ValueError'} if \typ{ValueError} is raised
\item Return \typ{'TypeError'} if \typ{TypeError} is raised
\end{enumerate}
For example:
\begin{lstlisting}
>>> safe_run(float, 'A')
'ValueError'
>>> def f(x): return x + 2
>>> safe_run(f, '2')
'TypeError'
>>> safe_run(float, '2')
'OK'
\end{lstlisting}
\end{frame}
\begin{frame}[fragile,plain]
\frametitle{Possible solution}
\begin{lstlisting}
def safe_run(f, x):
try:
f(x)
except ValueError:
return 'ValueError'
except TypeError:
return 'TypeError'
else:
return 'OK'
\end{lstlisting}
\end{frame}
\begin{frame}[plain, fragile]
\frametitle{Exercise: raising exceptions}
\begin{enumerate}
\item Write a function \typ{func} which takes a single integer argument
\item If \typ{x} is not a positive integer raise a \typ{ValueError}
\item If \typ{x} is not an integer type raise a \typ{TypeError}
\end{enumerate}
\end{frame}
\begin{frame}[fragile,plain]
\frametitle{Possible solution}
\small
\begin{lstlisting}
def func(x):
if type(x) != int:
raise TypeError('Expected int')
elif x < 0:
raise ValueError('Got negative int')
\end{lstlisting}
\end{frame}
\begin{frame}
\centering
\Huge
Thank you!
\end{frame}
\end{document}
\end{document}
|
